https://pythonlessonlab.com/ https://pythonlessonlab.com/learn/ https://pythonlessonlab.com/problems/ https://pythonlessonlab.com/about/ https://pythonlessonlab.com/contact/ https://pythonlessonlab.com/privacy/ https://pythonlessonlab.com/lessons/python-history/https://pythonlessonlab.com/assets/video-posters/python-history.jpgPython History: How It Started (1989–2008) | Lesson 00Trace Python's beginnings, its name, and the arrival of Python 3.https://www.youtube-nocookie.com/embed/hSFKWtoE_FU https://pythonlessonlab.com/lessons/hello-world/https://pythonlessonlab.com/assets/video-posters/hello-world.jpgPython Hello World: Your First Program | Lesson 01Run your first Python statements and recognize how Python displays output.https://www.youtube-nocookie.com/embed/wWIwt0hIE8E https://pythonlessonlab.com/lessons/variables-and-types/https://pythonlessonlab.com/assets/video-posters/variables-and-types.jpgPython Variables and Data Types Explained | Lesson 02Store values in variables and distinguish common Python data types.https://www.youtube-nocookie.com/embed/HeUk4WBQe0U https://pythonlessonlab.com/lessons/lists/https://pythonlessonlab.com/assets/video-posters/lists.jpgPython Lists: Index, Change, and Append | Lesson 03Create a list, access its items, and change its contents.https://www.youtube-nocookie.com/embed/7Ld1oCS14K8 https://pythonlessonlab.com/lessons/basic-operators/https://pythonlessonlab.com/assets/video-posters/basic-operators.jpgPython Operators: Arithmetic and Comparisons | Lesson 04Use Python operators to calculate values and compare results.https://www.youtube-nocookie.com/embed/-ior25w1Q34 https://pythonlessonlab.com/lessons/string-formatting/https://pythonlessonlab.com/assets/video-posters/string-formatting.jpgPython f-Strings: Format Text and Numbers | Lesson 05Build readable text that includes variables and formatted numbers.https://www.youtube-nocookie.com/embed/QtggirjET34 https://pythonlessonlab.com/lessons/basic-string-operations/https://pythonlessonlab.com/assets/video-posters/basic-string-operations.jpgPython String Methods and Slicing | Lesson 06Read characters and slices from strings and apply common string methods.https://www.youtube-nocookie.com/embed/VHlZzrKOsSk https://pythonlessonlab.com/lessons/conditions/https://pythonlessonlab.com/assets/video-posters/conditions.jpgPython if, elif, else Conditions | Lesson 07Use if, elif, and else in order: Python runs the first true branch and skips the rest. Compare values with ==, add colons, and indent each block.https://www.youtube-nocookie.com/embed/F1c4TqCIjH0 https://pythonlessonlab.com/lessons/loops/https://pythonlessonlab.com/assets/video-posters/loops.jpgPython for and while Loops | Lesson 08Repeat work with for and while loops and recognize when a loop stops.https://www.youtube-nocookie.com/embed/62XPceXqNlU https://pythonlessonlab.com/lessons/functions/https://pythonlessonlab.com/assets/video-posters/functions.jpgPython Functions: Parameters and Return | Lesson 09Define reusable code with parameters and return a result.https://www.youtube-nocookie.com/embed/hSJ-4shopTc https://pythonlessonlab.com/lessons/classes-and-objects/https://pythonlessonlab.com/assets/video-posters/classes-and-objects.jpgPython Classes and Objects: A First Example | Lesson 10Create a simple class and give each instance its own data.https://www.youtube-nocookie.com/embed/22cl8xk-paE https://pythonlessonlab.com/lessons/dictionaries/https://pythonlessonlab.com/assets/video-posters/dictionaries.jpgPython Dictionaries: Keys, Values, and get() | Lesson 11Store related values by key and retrieve or update them.https://www.youtube-nocookie.com/embed/944cyElWbXo https://pythonlessonlab.com/lessons/modules-and-packages/https://pythonlessonlab.com/assets/video-posters/modules-and-packages.jpgPython Modules and Packages: import math | Lesson 12Import a module and use a function from Python's standard library.https://www.youtube-nocookie.com/embed/GYI4HHUMFek https://pythonlessonlab.com/lessons/input-and-output/https://pythonlessonlab.com/assets/video-posters/input-and-output.jpgPython input() and Output: Convert Text Safely | Lesson 13Understand text input, convert it when needed, and present useful output.https://www.youtube-nocookie.com/embed/uZmv2hoSp2g https://pythonlessonlab.com/lessons/project-tip-calculator/https://pythonlessonlab.com/assets/video-posters/project-tip-calculator.jpgBuild a Python Tip Calculator | Practice Project 14Combine functions, arithmetic, and formatted output to split a restaurant bill.https://www.youtube-nocookie.com/embed/z8fi22vdVQk https://pythonlessonlab.com/lessons/project-number-guessing/https://pythonlessonlab.com/assets/video-posters/project-number-guessing.jpgBuild a Python Number Guessing Game | Project 15Use comparisons, a function, and a loop to evaluate guesses until the answer is found.https://www.youtube-nocookie.com/embed/Ds3UpsPr0m8 https://pythonlessonlab.com/lessons/project-text-analyzer/https://pythonlessonlab.com/assets/video-posters/project-text-analyzer.jpgBuild a Python Text Analyzer | Practice Project 16Combine string methods, a loop, and a dictionary to summarize a sentence.https://www.youtube-nocookie.com/embed/pihmMJVRFhI https://pythonlessonlab.com/lessons/tuples-and-sets/https://pythonlessonlab.com/assets/video-posters/tuples-and-sets.jpgPython Tuples and Sets Explained | Lesson 17Choose a tuple for a fixed group and a set for distinct values.https://www.youtube-nocookie.com/embed/gQ44cfd_D4o https://pythonlessonlab.com/lessons/exceptions/https://pythonlessonlab.com/assets/video-posters/exceptions.jpgPython Exceptions: try and except | Lesson 18Catch expected runtime errors and return useful messages without hiding unrelated bugs.https://www.youtube-nocookie.com/embed/KVlKrGeOMWk https://pythonlessonlab.com/lessons/files/https://pythonlessonlab.com/assets/video-posters/files.jpgRead and Write Files in Python | Lesson 19Write and read a UTF-8 text file with a context manager.https://www.youtube-nocookie.com/embed/wLnHtcd0ceI https://pythonlessonlab.com/lessons/installing-python-and-venv/https://pythonlessonlab.com/assets/video-posters/installing-python-and-venv.jpgInstall Python and Create a Virtual Environment | Lesson 20Set up a local Python installation and understand how a virtual environment isolates project packages.https://www.youtube-nocookie.com/embed/5ml4T5390pA https://pythonlessonlab.com/lessons/list-comprehensions/https://pythonlessonlab.com/assets/video-posters/list-comprehensions.jpgPython List Comprehensions: Build and Filter a ListBuild a new list from an iterable, add a filter, and explain the output before running it.https://www.youtube-nocookie.com/embed/wZ1y0aICv50 https://pythonlessonlab.com/lessons/function-arguments-and-scope/https://pythonlessonlab.com/assets/video-posters/function-arguments-and-scope.jpgPython Function Arguments, Return Values, and ScopePass values into a function, return a result, and distinguish local names from names in the caller.https://www.youtube-nocookie.com/embed/4st1GxuBM9c https://pythonlessonlab.com/lessons/json-and-csv/https://pythonlessonlab.com/assets/video-posters/json-and-csv.jpgRead and Write JSON and CSV in PythonSerialize and parse JSON, read CSV rows by header, and convert text fields deliberately.https://www.youtube-nocookie.com/embed/wD83KSB1uss https://pythonlessonlab.com/lessons/enumerate-and-zip/https://pythonlessonlab.com/assets/video-posters/enumerate-and-zip.jpgPython enumerate() and zip(): Number and Pair RowsPair related values and number them without manually managing an index.https://www.youtube-nocookie.com/embed/RQ96_ZGPHUE https://pythonlessonlab.com/lessons/dictionary-and-set-comprehensions/https://pythonlessonlab.com/assets/video-posters/dictionary-and-set-comprehensions.jpgPython Dictionary and Set Comprehensions | Real ExamplesBuild key/value mappings and unique-value sets from iterable data with readable comprehensions.https://www.youtube-nocookie.com/embed/BOp-t--1JcA https://pythonlessonlab.com/lessons/testing-python-functions/https://pythonlessonlab.com/assets/video-posters/testing-python-functions.jpgTest Python Functions with Assertions and unittestWrite repeatable tests that compare actual results with expected results and cover boundaries.https://www.youtube-nocookie.com/embed/dOT6PgEu7-g https://pythonlessonlab.com/lessons/dates-and-timedeltas/https://pythonlessonlab.com/assets/video-posters/dates-and-timedeltas.jpgPython Dates and Timedeltas | Calculate Dates CorrectlyParse a calendar date, shift it by a number of days, and produce a predictable ISO date string.https://www.youtube-nocookie.com/embed/cnfmneGng9w https://pythonlessonlab.com/lessons/project-csv-expense-tracker/https://pythonlessonlab.com/assets/video-posters/project-csv-expense-tracker.jpgBuild a Python CSV Expense Tracker | Mini ProjectRead CSV rows in memory and calculate reliable expense totals by category.https://www.youtube-nocookie.com/embed/A5l-ok68lrI https://pythonlessonlab.com/lessons/project-contact-book/https://pythonlessonlab.com/assets/video-posters/project-contact-book.jpgBuild a Python Contact Book | Mini ProjectStore, find, and update contacts with a dictionary and predictable name matching.https://www.youtube-nocookie.com/embed/bBvf1IgZLY8 https://pythonlessonlab.com/lessons/sorting-with-key/https://pythonlessonlab.com/assets/video-posters/sorting-with-key.jpgPython sorted() with key: Sort Products by PriceUse sorted(products, key=lambda item: item['price']) to return a new price-ordered list. Add reverse=True for descending order; equal-price items keep their input order.https://www.youtube-nocookie.com/embed/q8m9bkBqwwQ https://pythonlessonlab.com/lessons/pathlib-file-paths/https://pythonlessonlab.com/assets/video-posters/pathlib-file-paths.jpgPython pathlib: Fix Missing Folders and Save TextBuild and inspect paths with pathlib, create missing parent folders, and read or write UTF-8 text safely.https://www.youtube-nocookie.com/embed/KxxcIFVNrxI https://pythonlessonlab.com/lessons/regular-expressions/https://pythonlessonlab.com/assets/video-posters/regular-expressions.jpgPython Regex: Find Exact Codes Without Partial MatchesUse re.search() to get the first match or None, re.findall() to get all non-overlapping matches, and re.fullmatch() to validate an entire string.https://www.youtube-nocookie.com/embed/XjXjHP6EkcM https://pythonlessonlab.com/lessons/iterators-and-generators/https://pythonlessonlab.com/assets/video-posters/iterators-and-generators.jpgPython Generators: Why the Second Pass Is EmptyExplain one-pass iteration and write a generator that yields values as they are requested.https://www.youtube-nocookie.com/embed/G4H6x2JA5To https://pythonlessonlab.com/lessons/dataclasses/https://pythonlessonlab.com/assets/video-posters/dataclasses.jpgPython dataclasses: Fix Mutable List DefaultsUse @dataclass to generate an initializer, repr, and equality from annotated fields. Convert a record with asdict(), and use default_factory for each instance's list.https://www.youtube-nocookie.com/embed/H-YSJRR5LR4 https://pythonlessonlab.com/lessons/collections-counter-defaultdict/https://pythonlessonlab.com/assets/video-posters/collections-counter-defaultdict.jpgPython Counter and defaultdict: Count and Group DataCount repeated values and group records without writing fragile missing-key checks.https://www.youtube-nocookie.com/embed/3nhSMS9nj5E https://pythonlessonlab.com/lessons/type-hints-for-functions/https://pythonlessonlab.com/assets/video-posters/type-hints-for-functions.jpgPython Type Hints: What They Check (and What They Don't)Annotate function inputs and return values and explain what annotations do and do not enforce.https://www.youtube-nocookie.com/embed/1FMKdNfZk74 https://pythonlessonlab.com/lessons/decorators/https://pythonlessonlab.com/assets/video-posters/decorators.jpgPython Decorators: Wrap Functions Without Losing ResultsWrap a callable to add behavior while forwarding its arguments and result, keeping metadata, and tracking state per decorated function.https://www.youtube-nocookie.com/embed/QLfEG7CIgJ8 https://pythonlessonlab.com/lessons/context-managers/https://pythonlessonlab.com/assets/video-posters/context-managers.jpgPython Context Managers: Guaranteed Cleanup with withUse with to bound resource lifetime and create a context manager that releases a file even when the body raises.https://www.youtube-nocookie.com/embed/BDGn-hmDL6Q https://pythonlessonlab.com/lessons/itertools-for-data-pipelines/https://pythonlessonlab.com/assets/video-posters/itertools-for-data-pipelines.jpgPython itertools: Build Data Pipelines Without SurprisesCompose iterator tools to stream data, bound consumption, compute running totals, and understand consecutive grouping.https://www.youtube-nocookie.com/embed/IacxmwHVzVE https://pythonlessonlab.com/lessons/recursion-and-call-stack/https://pythonlessonlab.com/assets/video-posters/recursion-and-call-stack.jpgPython Recursion and the Call Stack: Find the Base CaseTrace recursive calls and write a function that stops correctly for empty and nested input.https://www.youtube-nocookie.com/embed/8C1GVN3le3g https://pythonlessonlab.com/lessons/structural-pattern-matching/https://pythonlessonlab.com/assets/video-posters/structural-pattern-matching.jpgPython match case: Structural Pattern Matching ExplainedChoose the first matching structural case and capture values from small event dictionaries.https://www.youtube-nocookie.com/embed/kaT6HN8lxgU https://pythonlessonlab.com/lessons/logging-in-python/https://pythonlessonlab.com/assets/video-posters/logging-in-python.jpgPython Logging: Replace Print with Useful LogsRecord messages at appropriate levels and filter them into a deterministic in-memory report.https://www.youtube-nocookie.com/embed/etsLsJ7O-f4 https://pythonlessonlab.com/lessons/asyncio-basics/https://pythonlessonlab.com/assets/video-posters/asyncio-basics.jpgPython asyncio Basics: Tasks, await, and Concurrent I/OWrite a coroutine and use asyncio.gather to collect independent simulated I/O results in input order.https://www.youtube-nocookie.com/embed/Dl0eJ2vKqbU https://pythonlessonlab.com/lessons/project-log-analyzer/https://pythonlessonlab.com/assets/video-posters/project-log-analyzer.jpgBuild a Python Log Analyzer: Parse and Count EventsTurn multiline log text into severity counts, error messages, and a count of malformed rows.https://www.youtube-nocookie.com/embed/fj7NO3BG6JQ https://pythonlessonlab.com/lessons/project-flashcard-quiz/https://pythonlessonlab.com/assets/video-posters/project-flashcard-quiz.jpgBuild a Python Flashcard Quiz with a ScoreGrade flashcard answers, report a score, and review missed questions without hiding a length mismatch.https://www.youtube-nocookie.com/embed/kV7SXfvwua8 https://pythonlessonlab.com/lessons/truthiness-none-and-identity/https://pythonlessonlab.com/assets/video-posters/truthiness-none-and-identity.jpgPython Truthiness, None, and Identity: Avoid Falsey BugsChoose between a truth test, equality, and identity without treating valid zero values as missing.https://www.youtube-nocookie.com/embed/9MWR9vooV1c https://pythonlessonlab.com/lessons/sequence-slicing-and-negative-steps/https://pythonlessonlab.com/assets/video-posters/sequence-slicing-and-negative-steps.jpgPython Slices and Negative Steps: Reverse and Window SequencesPredict and use sequence slices, including omitted bounds, negative indices, and a negative step.https://www.youtube-nocookie.com/embed/xqc8Wv30kwY https://pythonlessonlab.com/lessons/shallow-vs-deep-copy/https://pythonlessonlab.com/assets/video-posters/shallow-vs-deep-copy.jpgShallow vs Deep Copy in Python: Stop Changing the OriginalIdentify shared nested references and choose a copy depth that protects the original data.https://www.youtube-nocookie.com/embed/18wN5bk89UI https://pythonlessonlab.com/lessons/args-kwargs-and-unpacking/https://pythonlessonlab.com/assets/video-posters/args-kwargs-and-unpacking.jpgPython *args and **kwargs: Forward Arguments CorrectlyDistinguish variable positional arguments, named metadata, and a keyword-only option in one function.https://www.youtube-nocookie.com/embed/QZD8sn-CGhU https://pythonlessonlab.com/lessons/custom-exceptions-and-validation/https://pythonlessonlab.com/assets/video-posters/custom-exceptions-and-validation.jpgCustom Exceptions in Python: Validate and Raise ClearlyRaise a meaningful exception type for invalid input while preserving the underlying conversion cause.https://www.youtube-nocookie.com/embed/n6hBjSwJ8ak https://pythonlessonlab.com/lessons/reading-tracebacks-and-debugging/https://pythonlessonlab.com/assets/video-posters/reading-tracebacks-and-debugging.jpgRead Python Tracebacks: Find the Real ErrorUse traceback frames and exception causes to locate a bug and add useful context at the correct layer.https://www.youtube-nocookie.com/embed/n9A8fyiMLew https://pythonlessonlab.com/lessons/decimal-for-money/https://pythonlessonlab.com/assets/video-posters/decimal-for-money.jpgDecimal in Python: Calculate Money Without Float SurprisesRepresent decimal money from text and round a final amount to cents with an explicit rule.https://www.youtube-nocookie.com/embed/hVbi2e_WmHE https://pythonlessonlab.com/lessons/deque-queues-and-stacks/https://pythonlessonlab.com/assets/video-posters/deque-queues-and-stacks.jpgPython deque: Queue and Stack Patterns That ScaleChoose FIFO or LIFO deliberately and serve queued items efficiently without changing the caller's list.https://www.youtube-nocookie.com/embed/YgBxoHdcJNY https://pythonlessonlab.com/lessons/heapq-priority-queues/https://pythonlessonlab.com/assets/video-posters/heapq-priority-queues.jpgPython heapq: Build a Priority QueueUse heapq and an insertion counter to process lower numeric priorities first while preserving ties.https://www.youtube-nocookie.com/embed/s6NLKJmKkgE https://pythonlessonlab.com/lessons/bisect-binary-search/https://pythonlessonlab.com/assets/video-posters/bisect-binary-search.jpgPython bisect: Fast Search in Sorted ListsUse bisect_left on a sorted sequence to locate an insertion point even when the value is absent.https://www.youtube-nocookie.com/embed/i7qj1foxVeU https://pythonlessonlab.com/lessons/lru-cache-and-memoization/https://pythonlessonlab.com/assets/video-posters/lru-cache-and-memoization.jpgPython lru_cache: Memoize Expensive CallsUse functools.lru_cache on a deterministic function and verify both results and cache reuse.https://www.youtube-nocookie.com/embed/UsIH4ne5QUw https://pythonlessonlab.com/lessons/unicode-bytes-and-encodings/https://pythonlessonlab.com/assets/video-posters/unicode-bytes-and-encodings.jpgUnicode and Bytes in Python: Fix Encoding ErrorsKeep str and bytes distinct and perform an explicit UTF-8 round trip without changing the text.https://www.youtube-nocookie.com/embed/Q_SLdTr1_4g https://pythonlessonlab.com/lessons/time-zones-with-zoneinfo/https://pythonlessonlab.com/assets/video-posters/time-zones-with-zoneinfo.jpgTime Zones with zoneinfo in Python: Keep Times AwareConvert an aware UTC instant to a named local zone and observe daylight saving changes.https://www.youtube-nocookie.com/embed/5A2Ykq6HIXg https://pythonlessonlab.com/lessons/inheritance-vs-composition/https://pythonlessonlab.com/assets/video-posters/inheritance-vs-composition.jpgInheritance vs Composition in Python: Reuse Behavior SafelyBuild a service around an injected sender object so its behavior can change without subclassing the service.https://www.youtube-nocookie.com/embed/mq6fDR-gZA0 https://pythonlessonlab.com/lessons/properties-and-validation/https://pythonlessonlab.com/assets/video-posters/properties-and-validation.jpgPython Properties: Validate Attributes Without Breaking APIsProtect an object's state with a property setter and compute a read-only derived value.https://www.youtube-nocookie.com/embed/ShAjAPS4_gQ https://pythonlessonlab.com/lessons/environment-variables-and-configuration/https://pythonlessonlab.com/assets/video-posters/environment-variables-and-configuration.jpgPython Environment Variables: Safe ConfigurationConvert string-valued environment settings into a validated configuration with explicit defaults.https://www.youtube-nocookie.com/embed/rRxHSMeykv0 https://pythonlessonlab.com/lessons/http-apis-with-urllib/https://pythonlessonlab.com/assets/video-posters/http-apis-with-urllib.jpgFetch HTTP APIs with urllib in Python: Parse Responses SafelyDecode a JSON response through an injected opener and validate its shape without requiring a live API.https://www.youtube-nocookie.com/embed/684uhZpDDfk https://pythonlessonlab.com/lessons/special-methods-repr-eq-len/https://pythonlessonlab.com/assets/video-posters/special-methods-repr-eq-len.jpgPython Special Methods: repr, eq, and lenImplement three special methods with clear value semantics and handle unsupported comparisons correctly.https://www.youtube-nocookie.com/embed/mnWZPR5yVgw https://pythonlessonlab.com/lessons/mocking-dependencies-in-tests/https://pythonlessonlab.com/assets/video-posters/mocking-dependencies-in-tests.jpgMock Dependencies in Python Tests: Isolate BehaviorWrite a function with an injected dependency and test its return value and interaction without external I/O.https://www.youtube-nocookie.com/embed/MeVvy_iiPEw https://pythonlessonlab.com/lessons/argparse-command-line-tools/https://pythonlessonlab.com/assets/video-posters/argparse-command-line-tools.jpgargparse in Python: Build a Useful CLIDefine a repeatable argument parser for a report command and validate its parsed options.https://www.youtube-nocookie.com/embed/72tsgsSQNBI https://pythonlessonlab.com/lessons/floating-point-comparisons-math-isclose/https://pythonlessonlab.com/assets/video-posters/floating-point-comparisons-math-isclose.jpgCompare Python Floats with math.isclose: Tolerances That MatterUse explicit numerical tolerances for approximate float results, including comparisons near zero.https://www.youtube-nocookie.com/embed/uBqgibcb48Y https://pythonlessonlab.com/lessons/csv-dictreader-and-row-validation/https://pythonlessonlab.com/assets/video-posters/csv-dictreader-and-row-validation.jpgRead CSV Rows with DictReader and Validate Missing DataRead CSV by field name and validate its header, text, and numeric fields before using a row.https://www.youtube-nocookie.com/embed/0wO5u_XS9MY https://pythonlessonlab.com/lessons/json-lines-streaming/https://pythonlessonlab.com/assets/video-posters/json-lines-streaming.jpgProcess JSON Lines in Python Without Loading Every RecordDistinguish one JSON document from line-delimited records and validate each decoded object.https://www.youtube-nocookie.com/embed/wFrk5Uzs4jU https://pythonlessonlab.com/lessons/statistics-mean-median-outliers/https://pythonlessonlab.com/assets/video-posters/statistics-mean-median-outliers.jpgMean, Median, and Outliers in Python: Choose the Right SummaryCalculate mean and median and explain why an extreme value affects them differently.https://www.youtube-nocookie.com/embed/x-LojYDgyTM https://pythonlessonlab.com/lessons/text-normalization-unicodedata/https://pythonlessonlab.com/assets/video-posters/text-normalization-unicodedata.jpgNormalize Unicode Text in Python Before Comparing StringsCreate a documented comparison key using Unicode NFC normalization and casefold.https://www.youtube-nocookie.com/embed/IXFJsNp-SoU https://pythonlessonlab.com/lessons/enums-for-states/https://pythonlessonlab.com/assets/video-posters/enums-for-states.jpgUse Python Enums for Valid States Instead of Magic StringsRepresent a small workflow with Enum members and convert untrusted text at its boundary.https://www.youtube-nocookie.com/embed/hUVZjdwelfA https://pythonlessonlab.com/lessons/closures-and-nonlocal/https://pythonlessonlab.com/assets/video-posters/closures-and-nonlocal.jpgPython Closures and nonlocal: Preserve State DeliberatelyReturn a closure that remembers state and use nonlocal only when rebinding that state.https://www.youtube-nocookie.com/embed/hQMVw4k1kYc https://pythonlessonlab.com/lessons/classmethods-and-staticmethods/https://pythonlessonlab.com/assets/video-posters/classmethods-and-staticmethods.jpgPython classmethod vs staticmethod: Choose by ResponsibilityUse a classmethod for an alternative constructor and a staticmethod for class-related validation without instance state.https://www.youtube-nocookie.com/embed/cR2EDQavf7Y https://pythonlessonlab.com/lessons/exception-chaining/https://pythonlessonlab.com/assets/video-posters/exception-chaining.jpgPython Exception Chaining: Preserve the Original CauseRaise a domain-specific error from a lower-level exception without losing the original cause.https://www.youtube-nocookie.com/embed/l3fSZJ0glsI https://pythonlessonlab.com/lessons/unittest-fixtures-and-subtests/https://pythonlessonlab.com/assets/video-posters/unittest-fixtures-and-subtests.jpgPython unittest Fixtures and subTest: Test Multiple Cases ClearlyUse setUp for fresh test data and subTest to label multiple inputs within a unittest method.https://www.youtube-nocookie.com/embed/LDdzR3tx5fk https://pythonlessonlab.com/lessons/urlparse-and-query-parameters/https://pythonlessonlab.com/assets/video-posters/urlparse-and-query-parameters.jpgParse URLs and Query Parameters Safely with urllib.parseReplace one URL query parameter without losing existing parameters or the fragment.https://www.youtube-nocookie.com/embed/sz29AeZn6HE https://pythonlessonlab.com/lessons/html-escaping-safe-output/https://pythonlessonlab.com/assets/video-posters/html-escaping-safe-output.jpgEscape HTML in Python: Render User Text as TextRender untrusted text as visible HTML text without treating its angle brackets as markup.https://www.youtube-nocookie.com/embed/PKvFeSugaw0 https://pythonlessonlab.com/lessons/hashlib-content-checksums/https://pythonlessonlab.com/assets/video-posters/hashlib-content-checksums.jpgVerify File Content with Python hashlib ChecksumsCalculate a deterministic SHA-256 checksum for text and detect when its content changes.https://www.youtube-nocookie.com/embed/V9HBtGCr0w8 https://pythonlessonlab.com/lessons/configparser-ini-files/https://pythonlessonlab.com/assets/video-posters/configparser-ini-files.jpgRead INI Configuration with Python configparserParse a small INI configuration and return typed, validated job settings.https://www.youtube-nocookie.com/embed/gpSklk-Z2DU https://pythonlessonlab.com/lessons/zipfile-archives/https://pythonlessonlab.com/assets/video-posters/zipfile-archives.jpgCreate and Inspect ZIP Archives with Python zipfileCreate a ZIP archive from simple named text entries and inspect its contents without extraction.https://www.youtube-nocookie.com/embed/DEg6AwS4u2I https://pythonlessonlab.com/lessons/project-inventory-reorder-planner/https://pythonlessonlab.com/assets/video-posters/project-inventory-reorder-planner.jpgBuild a Python Inventory Reorder Planner with TestsTurn validated stock records into a stable, explainable reorder plan without changing the source records.https://www.youtube-nocookie.com/embed/KB92NDSCTNQ https://pythonlessonlab.com/lessons/project-booking-conflict-detector/https://pythonlessonlab.com/assets/video-posters/project-booking-conflict-detector.jpgBuild a Python Booking Conflict DetectorDetect overlapping bookings with a half-open time rule and return conflict pairs in input order.https://www.youtube-nocookie.com/embed/rd8YdWSzTLQ https://pythonlessonlab.com/lessons/project-csv-import-validator/https://pythonlessonlab.com/assets/video-posters/project-csv-import-validator.jpgBuild a Python CSV Import Validator with Error ReportsValidate an entire CSV import and return accepted records alongside deterministic row-specific errors.https://www.youtube-nocookie.com/embed/mD8hQrvfB6Y https://pythonlessonlab.com/lessons/project-archive-manifest-verifier/https://pythonlessonlab.com/assets/video-posters/project-archive-manifest-verifier.jpgBuild a Python Archive Manifest VerifierVerify a small in-memory ZIP against an expected manifest without writing archive members to disk.https://www.youtube-nocookie.com/embed/rsojtRdOatE https://pythonlessonlab.com/lessons/project-offline-web-crawler/https://pythonlessonlab.com/assets/video-posters/project-offline-web-crawler.jpgBuild an Offline Python Web Crawler on Fixture PagesTraverse an in-memory graph of HTML page fixtures in stable breadth-first order without network requests.https://www.youtube-nocookie.com/embed/Hfr-u_UPODc https://pythonlessonlab.com/lessons/sqlite3-parameterized-queries/https://pythonlessonlab.com/assets/video-posters/sqlite3-parameterized-queries.jpgSQLite Parameterized Queries and Transactions in PythonUse SQLite placeholders for values and understand when a transaction commits or rolls back.https://www.youtube-nocookie.com/embed/bAgaCqMGViI https://pythonlessonlab.com/lessons/secrets-secure-tokens/https://pythonlessonlab.com/assets/video-posters/secrets-secure-tokens.jpgGenerate Secure Random Tokens with Python secretsCreate unpredictable URL-safe tokens with an explicit minimum random-byte requirement.https://www.youtube-nocookie.com/embed/rSegZaCfYWI https://pythonlessonlab.com/lessons/random-reproducible-simulations/https://pythonlessonlab.com/assets/video-posters/random-reproducible-simulations.jpgReproducible Simulations with Python random.RandomRun a repeatable simulation with an independent random generator and validated trial count.https://www.youtube-nocookie.com/embed/V_YRD7TXZnU https://pythonlessonlab.com/lessons/collections-chainmap-layered-config/https://pythonlessonlab.com/assets/video-posters/collections-chainmap-layered-config.jpgLayer Configuration with Python collections.ChainMapBuild a shallow configuration snapshot with explicit precedence across three mappings.https://www.youtube-nocookie.com/embed/iPntiei6WEw https://pythonlessonlab.com/lessons/tempfile-atomic-writes/https://pythonlessonlab.com/assets/video-posters/tempfile-atomic-writes.jpgAtomic File Writes with tempfile and os.replace in PythonReplace a file only after a complete new value has been written to a temporary file.https://www.youtube-nocookie.com/embed/mhhhAheBhP8 https://pythonlessonlab.com/lessons/xml-elementtree/https://pythonlessonlab.com/assets/video-posters/xml-elementtree.jpgParse and Build XML with Python ElementTreeUse ElementTree to parse trusted small XML and create escaped XML elements.https://www.youtube-nocookie.com/embed/qe3kgw8IZ9g https://pythonlessonlab.com/lessons/difflib-text-diffs/https://pythonlessonlab.com/assets/video-posters/difflib-text-diffs.jpgCompare Text and Produce Unified Diffs with Python difflibCreate a unified diff for two text versions with stable labels and preserved line endings.https://www.youtube-nocookie.com/embed/3QCUB0C0h2Q https://pythonlessonlab.com/lessons/fractions-exact-ratios/https://pythonlessonlab.com/assets/video-posters/fractions-exact-ratios.jpgExact Ratios with Python FractionUse Fraction for exact rational ratios and reject ambiguous float input.https://www.youtube-nocookie.com/embed/Wu3wDui2bo8 https://pythonlessonlab.com/lessons/ipaddress-network-validation/https://pythonlessonlab.com/assets/video-posters/ipaddress-network-validation.jpgValidate IP Addresses and Networks with Python ipaddressParse addresses and CIDR networks, then decide membership with ipaddress rather than text matching.https://www.youtube-nocookie.com/embed/__dgfHNzcEc https://pythonlessonlab.com/lessons/shutil-copy-move/https://pythonlessonlab.com/assets/video-posters/shutil-copy-move.jpgCopy and Move Files Safely with Python shutilCopy a file without deleting its source, then move a file with explicit collision handling.https://www.youtube-nocookie.com/embed/TrpHuUcdZS4 https://pythonlessonlab.com/lessons/functools-partial-callbacks/https://pythonlessonlab.com/assets/video-posters/functools-partial-callbacks.jpgConfigure Callbacks with Python functools.partialBuild a callable with selected arguments fixed while keeping other arguments open.https://www.youtube-nocookie.com/embed/3UuJ9StWKJo https://pythonlessonlab.com/lessons/typing-protocols/https://pythonlessonlab.com/assets/video-posters/typing-protocols.jpgStructural Interfaces with Python typing.ProtocolUse a Protocol to describe interchangeable objects and understand what runtime checks do and do not prove.https://www.youtube-nocookie.com/embed/91Xsqivlb2A https://pythonlessonlab.com/lessons/inspect-signatures-and-binding/https://pythonlessonlab.com/assets/video-posters/inspect-signatures-and-binding.jpgInspect Python Function Signatures and Bind ArgumentsUse inspect.signature and bind to validate a proposed function call without running the function.https://www.youtube-nocookie.com/embed/GZcMRnwOrM0 https://pythonlessonlab.com/lessons/ast-literal-eval-vs-eval/https://pythonlessonlab.com/assets/video-posters/ast-literal-eval-vs-eval.jpgParse Python Literals Safely with ast.literal_evalUse ast.literal_eval for literal syntax while enforcing an application-specific shape and size limit.https://www.youtube-nocookie.com/embed/q-kbC2tJ5CY https://pythonlessonlab.com/lessons/topological-sort-dependencies/https://pythonlessonlab.com/assets/video-posters/topological-sort-dependencies.jpgTopological Sort for Task Dependencies in PythonReturn tasks in an order that places every prerequisite before its dependent task.https://www.youtube-nocookie.com/embed/__fxBlxJIEI https://pythonlessonlab.com/lessons/email-message-parse-build/https://pythonlessonlab.com/assets/video-posters/email-message-parse-build.jpgBuild and Parse Email Messages Offline with PythonConstruct a plain-text EmailMessage and parse its bytes while keeping transport separate.https://www.youtube-nocookie.com/embed/IIFsnCOmVdU https://pythonlessonlab.com/lessons/base64-binary-text/https://pythonlessonlab.com/assets/video-posters/base64-binary-text.jpgEncode Binary Data with Python base64Convert text to bytes before Base64 encoding and validate decoded input before using it.https://www.youtube-nocookie.com/embed/unQs9PIEI6M https://pythonlessonlab.com/lessons/hmac-authenticated-messages/https://pythonlessonlab.com/assets/video-posters/hmac-authenticated-messages.jpgAuthenticate Messages with Python hmacSign a byte message with HMAC-SHA256 and verify it using a shared secret key.https://www.youtube-nocookie.com/embed/pdV40fBX3Yc https://pythonlessonlab.com/lessons/uuid-stable-identifiers/https://pythonlessonlab.com/assets/video-posters/uuid-stable-identifiers.jpgCreate Stable and Random UUIDs in PythonBuild a reproducible UUID from a namespace and normalized name, and distinguish it from a random UUID.https://www.youtube-nocookie.com/embed/qaflL1gwkao https://pythonlessonlab.com/lessons/gzip-compressed-data/https://pythonlessonlab.com/assets/video-posters/gzip-compressed-data.jpgCompress Text and Bytes with Python gzipCompress UTF-8 text into gzip bytes and recover the original text.https://www.youtube-nocookie.com/embed/5jA7WjxBPRA https://pythonlessonlab.com/lessons/struct-binary-records/https://pythonlessonlab.com/assets/video-posters/struct-binary-records.jpgPack Binary Records with Python structPack an unsigned identifier and status byte into a stable three-byte record.https://www.youtube-nocookie.com/embed/q1msu9AOtbk https://pythonlessonlab.com/lessons/io-stringio-text-streams/https://pythonlessonlab.com/assets/video-posters/io-stringio-text-streams.jpgTest Text Streams with Python StringIOPass a StringIO stream into a function and rewind it before a second read.https://www.youtube-nocookie.com/embed/N2SRpdvlm-Q https://pythonlessonlab.com/lessons/tomllib-read-config/https://pythonlessonlab.com/assets/video-posters/tomllib-read-config.jpgRead TOML Configuration with Python tomllibLoad a TOML configuration string and validate a required positive integer setting.https://www.youtube-nocookie.com/embed/3xt9Sbil1ZI https://pythonlessonlab.com/lessons/glob-file-patterns/https://pythonlessonlab.com/assets/video-posters/glob-file-patterns.jpgFind Files with Python glob and fnmatchSelect matching file names from a known list using fnmatchcase and deterministic sorting.https://www.youtube-nocookie.com/embed/znE8ayAK42M https://pythonlessonlab.com/lessons/timeit-benchmarking/https://pythonlessonlab.com/assets/video-posters/timeit-benchmarking.jpgBenchmark Tiny Python Functions with timeitCompute a per-call benchmark from repeated timeit runs without claiming universal speed.https://www.youtube-nocookie.com/embed/iAikyQIw3fA https://pythonlessonlab.com/lessons/graph-breadth-first-search/https://pythonlessonlab.com/assets/video-posters/graph-breadth-first-search.jpgFind a Shortest Unweighted Path with BFSReturn a shortest path in an unweighted adjacency-list graph using a FIFO queue.https://www.youtube-nocookie.com/embed/bUZ6wCWYtXE https://pythonlessonlab.com/lessons/graph-depth-first-cycle-detection/https://pythonlessonlab.com/assets/video-posters/graph-depth-first-cycle-detection.jpgDetect Directed Graph Cycles with DFSDetect whether a directed adjacency-list graph contains a cycle.https://www.youtube-nocookie.com/embed/ViiJt2WyfxM https://pythonlessonlab.com/lessons/dynamic-programming-coin-change/https://pythonlessonlab.com/assets/video-posters/dynamic-programming-coin-change.jpgSolve Coin Change with Dynamic ProgrammingReturn the minimum number of positive-denomination coins for a target amount, or None if unreachable.https://www.youtube-nocookie.com/embed/Ux3MBGRVR7w https://pythonlessonlab.com/lessons/sliding-window-moving-average/https://pythonlessonlab.com/assets/video-posters/sliding-window-moving-average.jpgCompute a Moving Average with a Sliding WindowReturn every fixed-size moving average with one pass and a running sum.https://www.youtube-nocookie.com/embed/4_D2nNVkXYE https://pythonlessonlab.com/lessons/union-find-connected-components/https://pythonlessonlab.com/assets/video-posters/union-find-connected-components.jpgCount Connected Components with Union-FindCount connected components in an undirected graph using a disjoint-set structure.https://www.youtube-nocookie.com/embed/573O51_Oi7w https://pythonlessonlab.com/lessons/prefix-sums-range-queries/https://pythonlessonlab.com/assets/video-posters/prefix-sums-range-queries.jpgAnswer Range Sum Queries with Prefix SumsBuild prefix totals and compute sums for half-open index ranges.https://www.youtube-nocookie.com/embed/ahedUIpli-E https://pythonlessonlab.com/lessons/regex-capture-groups-and-substitution/https://pythonlessonlab.com/assets/video-posters/regex-capture-groups-and-substitution.jpgCapture and Replace Text with Python RegexUse named capture groups and a re.sub callback to transform complete order codes without changing unrelated text.https://www.youtube-nocookie.com/embed/8sU4iknIunw https://pythonlessonlab.com/lessons/dataclass-post-init-validation/https://pythonlessonlab.com/assets/video-posters/dataclass-post-init-validation.jpgValidate Dataclasses with __post_init__Reject reversed range bounds and calculate a derived span immediately after a generated dataclass initializer runs.https://www.youtube-nocookie.com/embed/KljtWebY6A8 https://pythonlessonlab.com/lessons/asyncio-taskgroup-and-cancellation/https://pythonlessonlab.com/assets/video-posters/asyncio-taskgroup-and-cancellation.jpgManage Async Tasks with TaskGroup and CancellationUse asyncio.TaskGroup to wait for related tasks, retrieve results in input order, and understand sibling cancellation after failure.https://www.youtube-nocookie.com/embed/C5W_G5P0Egk https://pythonlessonlab.com/lessons/dictionary-merge-conflict-policies/https://pythonlessonlab.com/assets/video-posters/dictionary-merge-conflict-policies.jpgMerge Dictionaries and Handle Duplicate KeysMerge dictionaries while making duplicate-key behavior explicit and leaving inputs unchanged.https://www.youtube-nocookie.com/embed/TwodKIsNhyk https://pythonlessonlab.com/lessons/set-operations-for-comparing-groups/https://pythonlessonlab.com/assets/video-posters/set-operations-for-comparing-groups.jpgCompare Groups with Python Set OperationsCompare two groups with union, intersection, and difference while returning deterministic sorted results.https://www.youtube-nocookie.com/embed/xYDPerDhSug https://pythonlessonlab.com/lessons/nested-json-safe-extraction/https://pythonlessonlab.com/assets/video-posters/nested-json-safe-extraction.jpgRead Nested JSON with Explicit Missing-Field RulesExtract a city from nested JSON data while distinguishing a missing optional value from an invalid object shape.https://www.youtube-nocookie.com/embed/iVXXpCho_nU https://pythonlessonlab.com/lessons/csv-quoting-and-dialects/https://pythonlessonlab.com/assets/video-posters/csv-quoting-and-dialects.jpgRead and Write CSV with Quoting and DialectsRead and write CSV records containing commas and quotation marks without splitting lines manually.https://www.youtube-nocookie.com/embed/NVkqXsZEzNU https://pythonlessonlab.com/lessons/custom-json-encoding-and-decoding/https://pythonlessonlab.com/assets/video-posters/custom-json-encoding-and-decoding.jpgSerialize Datetime and Decimal Values to JSONSerialize datetime and Decimal values to JSON with an explicit representation and reject unsupported types.https://www.youtube-nocookie.com/embed/4iu6x4NMd6E https://pythonlessonlab.com/lessons/project-gradebook-report/https://pythonlessonlab.com/assets/video-posters/project-gradebook-report.jpgProject: Build a Gradebook ReportBuild a small gradebook report from CSV data with validated scores, averages, and deterministic ranking.https://www.youtube-nocookie.com/embed/GEWF-rTeUhY https://pythonlessonlab.com/lessons/command-line-output-and-exit-codes/https://pythonlessonlab.com/assets/video-posters/command-line-output-and-exit-codes.jpgWrite Clear CLI Output and Exit CodesSeparate successful CLI output from error diagnostics and return meaningful exit codes.https://www.youtube-nocookie.com/embed/3LgTyF5iwAI https://pythonlessonlab.com/lessons/shlex-parse-command-input/https://pythonlessonlab.com/assets/video-posters/shlex-parse-command-input.jpgParse Quoted Commands with Python shlexParse a small command line while preserving quoted arguments and rejecting malformed input.https://www.youtube-nocookie.com/embed/u444mBBG_84 https://pythonlessonlab.com/lessons/project-command-menu/https://pythonlessonlab.com/assets/video-posters/project-command-menu.jpgBuild a Safe Python Text Command MenuParse and execute add, remove, and show commands against an in-memory inventory.https://www.youtube-nocookie.com/embed/clTihakau8U https://pythonlessonlab.com/lessons/functools-singledispatch/https://pythonlessonlab.com/assets/video-posters/functools-singledispatch.jpgDispatch by Type with functools.singledispatchRegister type-specific handlers and distinguish bool from int.https://www.youtube-nocookie.com/embed/aod9scSLCd4 https://pythonlessonlab.com/lessons/cached-property-and-invalidation/https://pythonlessonlab.com/assets/video-posters/cached-property-and-invalidation.jpgCache and Invalidate Python PropertiesCache an expensive derived value and invalidate it whenever its inputs change.https://www.youtube-nocookie.com/embed/cfTtSKzqZEw https://pythonlessonlab.com/lessons/callable-objects-and-state/https://pythonlessonlab.com/assets/video-posters/callable-objects-and-state.jpgBuild Stateful Callable Objects in PythonUse __call__ to make a validated counter object invokable while it keeps its own state.https://www.youtube-nocookie.com/embed/iUnxoFAlycU https://pythonlessonlab.com/lessons/io-bytesio-and-binary-streams/https://pythonlessonlab.com/assets/video-posters/io-bytesio-and-binary-streams.jpgRead Binary Records with Python BytesIORead a length-prefixed binary record from BytesIO and reject incomplete payloads.https://www.youtube-nocookie.com/embed/UxaHR7vDEjg https://pythonlessonlab.com/lessons/files-line-endings-and-encoding/https://pythonlessonlab.com/assets/video-posters/files-line-endings-and-encoding.jpgHandle Python File Encodings and Line EndingsDecode UTF-8 bytes and split lines consistently across LF, CRLF, and CR endings.https://www.youtube-nocookie.com/embed/3_F7bH3e9ew https://pythonlessonlab.com/lessons/project-duplicate-file-scanner/https://pythonlessonlab.com/assets/video-posters/project-duplicate-file-scanner.jpgBuild an Offline Duplicate File ScannerGroup equal byte contents by path and explain how to extend the algorithm to real files.https://www.youtube-nocookie.com/embed/D0LEufzDxv4 https://pythonlessonlab.com/lessons/calendar-month-boundaries/https://pythonlessonlab.com/assets/video-posters/calendar-month-boundaries.jpgFind Month Start and End Dates in PythonReturn the first and last date of a month, including leap-year February.https://www.youtube-nocookie.com/embed/ttpkXdqVxh4 https://pythonlessonlab.com/lessons/datetime-strptime-and-strftime/https://pythonlessonlab.com/assets/video-posters/datetime-strptime-and-strftime.jpgParse and Format UTC Timestamps in PythonValidate a fixed UTC timestamp format before producing an ISO-style output string.https://www.youtube-nocookie.com/embed/d4zgiIvNrtM https://pythonlessonlab.com/lessons/project-habit-streak-analyzer/https://pythonlessonlab.com/assets/video-posters/project-habit-streak-analyzer.jpgBuild a Python Habit Streak AnalyzerFind the longest run of consecutive calendar dates in a list of habit check-ins.https://www.youtube-nocookie.com/embed/q8GxQ08fbyU https://pythonlessonlab.com/lessons/statistics-quantiles-and-percentiles/https://pythonlessonlab.com/assets/video-posters/statistics-quantiles-and-percentiles.jpgCalculate Quantiles and Percentiles with PythonCalculate and interpret inclusive quartiles for a numeric dataset with an explicit method.https://www.youtube-nocookie.com/embed/kGeS-qAlpkA https://pythonlessonlab.com/lessons/random-weighted-sampling/https://pythonlessonlab.com/assets/video-posters/random-weighted-sampling.jpgUse Weighted Random Sampling in PythonDraw one outcome according to validated nonnegative weights using an injected random generator.https://www.youtube-nocookie.com/embed/NI0O2fpp-S8 https://pythonlessonlab.com/lessons/project-survey-summarizer/https://pythonlessonlab.com/assets/video-posters/project-survey-summarizer.jpgBuild a Python Survey Response SummarizerNormalize optional survey answers and compute sorted choice counts plus an optional rating average.https://www.youtube-nocookie.com/embed/MXQ3Qj2CVBg https://pythonlessonlab.com/lessons/algorithmic-complexity-in-practice/https://pythonlessonlab.com/assets/video-posters/algorithmic-complexity-in-practice.jpgUnderstand Python Algorithmic Complexity with Measured InputsMeasure how comparison counts grow for linear and binary search on increasing sorted inputs.https://www.youtube-nocookie.com/embed/oXwd04MGq3M https://pythonlessonlab.com/lessons/two-pointer-technique/https://pythonlessonlab.com/assets/video-posters/two-pointer-technique.jpgSolve Sorted-List Pair Sums with Two PointersFind a pair that reaches a target sum in a sorted list without testing every pair.https://www.youtube-nocookie.com/embed/6S3WXWtMBrk https://pythonlessonlab.com/lessons/backtracking-combinations-and-pruning/https://pythonlessonlab.com/assets/video-posters/backtracking-combinations-and-pruning.jpgFind Combinations with Python Backtracking and PruningGenerate unique positive-integer combinations that sum to a target while pruning impossible branches.https://www.youtube-nocookie.com/embed/hv700j1sqKM https://pythonlessonlab.com/lessons/http-json-response-validation/https://pythonlessonlab.com/assets/video-posters/http-json-response-validation.jpgValidate JSON from HTTP Responses in PythonValidate an HTTP-like response's status, JSON syntax, and expected field types before using its data.https://www.youtube-nocookie.com/embed/I3RVmO1wsw0 https://pythonlessonlab.com/lessons/retries-timeouts-and-backoff/https://pythonlessonlab.com/assets/video-posters/retries-timeouts-and-backoff.jpgRetry Transient Failures with Timeouts and Backoff in PythonRetry only transient local failures with a bounded exponential delay schedule.https://www.youtube-nocookie.com/embed/gO3ceIf-MIg https://pythonlessonlab.com/lessons/project-offline-api-client/https://pythonlessonlab.com/assets/video-posters/project-offline-api-client.jpgBuild an Offline Python API Client SimulatorBuild a deterministic offline client that retries temporary failures, validates user JSON, and caches only successful records.https://www.youtube-nocookie.com/embed/uHVYHSieYo0 https://pythonlessonlab.com/lessons/python-typeddict-required-optional-keys/https://pythonlessonlab.com/assets/video-posters/python-typeddict-required-optional-keys.jpgPython TypedDict: Required and Optional KeysModel a dictionary record with one required key and one optional key, then use it without assuming TypedDict validates values at runtime.https://www.youtube-nocookie.com/embed/n9vzHPg9JjM https://pythonlessonlab.com/lessons/pillow-resize-image-aspect-ratio/https://pythonlessonlab.com/assets/video-posters/pillow-resize-image-aspect-ratio.jpgPillow Resize Image Without Losing Aspect RatioResize an image into a maximum width and height without distortion, upscaling, or changing the original image.https://www.youtube-nocookie.com/embed/OsgYbv-tZ3M https://pythonlessonlab.com/lessons/pandas-groupby-multiple-columns/https://pythonlessonlab.com/assets/video-posters/pandas-groupby-multiple-columns.jpgPandas GroupBy Multiple Columns with Named AggregationsSummarize sales by region and product, with separate total amount and distinct order count columns.https://www.youtube-nocookie.com/embed/2efHBDvqlqY https://pythonlessonlab.com/lessons/pandas-merge-on-multiple-columns/https://pythonlessonlab.com/assets/video-posters/pandas-merge-on-multiple-columns.jpgPandas Merge on Multiple Columns Without Duplicate MatchesJoin orders with regional prices using both SKU and region, rejecting duplicate lookup keys and null join keys.https://www.youtube-nocookie.com/embed/Ux2-ty4186Q https://pythonlessonlab.com/lessons/pandas-drop-duplicates-by-column/https://pythonlessonlab.com/assets/video-posters/pandas-drop-duplicates-by-column.jpgPandas Drop Duplicates by Column and Keep the Latest RowDeduplicate records by email while retaining the latest timestamped row and leaving the input unchanged.https://www.youtube-nocookie.com/embed/obak0ZsedTc https://pythonlessonlab.com/lessons/python-create-temp-file/https://pythonlessonlab.com/assets/video-posters/python-create-temp-file.jpgPython Create Temp File with NamedTemporaryFileCreate a UTF-8 temporary file, read it from the correct cursor position, and clean it up automatically.https://www.youtube-nocookie.com/embed/rDNRq5zBU2E https://pythonlessonlab.com/lessons/python-rotating-file-handler/https://pythonlessonlab.com/assets/video-posters/python-rotating-file-handler.jpgPython Rotating File Handler: Limit Log File SizeRotate a UTF-8 log file by byte size and retain a bounded number of backups.https://www.youtube-nocookie.com/embed/_sI3nRkxJWo https://pythonlessonlab.com/lessons/python-argparse-subcommands/https://pythonlessonlab.com/assets/video-posters/python-argparse-subcommands.jpgPython argparse Subcommands with add_subparsersGive add and list commands separate arguments and reject a missing or incomplete command.https://www.youtube-nocookie.com/embed/Nzpa58nMo9k https://pythonlessonlab.com/lessons/python-concurrent-futures-as-completed/https://pythonlessonlab.com/assets/video-posters/python-concurrent-futures-as-completed.jpgPython concurrent.futures as_completed: Handle Results as They FinishConsume futures in completion order, associate each result with its input, and handle individual failures.https://www.youtube-nocookie.com/embed/21i_MS37dh8 https://pythonlessonlab.com/lessons/python-subprocess-run-command/https://pythonlessonlab.com/assets/video-posters/python-subprocess-run-command.jpgPython subprocess.run Command: Capture Output SafelyRun a known local Python child process with separate arguments, capture output, and handle status and timeout.https://www.youtube-nocookie.com/embed/GxxJWAsclVY https://pythonlessonlab.com/lessons/python-zipfile-extract-safely/https://pythonlessonlab.com/assets/video-posters/python-zipfile-extract-safely.jpgPython zipfile extract: unpack selected files safelyInspect ZIP members, allow only expected text files, and extract them into one chosen directory.https://www.youtube-nocookie.com/embed/2bZqwl1cP1c https://pythonlessonlab.com/lessons/fastapi-request-body-validation/https://pythonlessonlab.com/assets/video-posters/fastapi-request-body-validation.jpgFastAPI request body: validate JSON with a Pydantic modelDeclare a POST request body, separate it from path parameters, and understand automatic 422 validation responses.https://www.youtube-nocookie.com/embed/eBG8Ywpp9gg https://pythonlessonlab.com/lessons/beautifulsoup-parse-html-table/https://pythonlessonlab.com/assets/video-posters/beautifulsoup-parse-html-table.jpgBeautifulSoup parse table: extract HTML rows into Python recordsSelect one HTML table, read its header and cells, and turn rows into records without confusing nested tables.https://www.youtube-nocookie.com/embed/-4WvWlksb_0 https://pythonlessonlab.com/lessons/python-cprofile-example/https://pythonlessonlab.com/assets/video-posters/python-cprofile-example.jpgPython cProfile example: find slow functions and read pstatsProfile a function, sort cumulative time, and distinguish call counts from elapsed time.https://www.youtube-nocookie.com/embed/TaSm707fM-8 https://pythonlessonlab.com/lessons/openpyxl-read-excel-python/https://pythonlessonlab.com/assets/video-posters/openpyxl-read-excel-python.jpgopenpyxl read Excel in Python: rows, headers, and valuesRead an .xlsx workbook with openpyxl and turn a sheet with headers into validated records.https://www.youtube-nocookie.com/embed/FJgdbf-4-1E https://pythonlessonlab.com/lessons/numpy-reshape-array-dimensions/https://pythonlessonlab.com/assets/video-posters/numpy-reshape-array-dimensions.jpgNumPy reshape: Change Array Dimensions Without Shape ErrorsReshape a one-dimensional NumPy array into a chosen number of columns, with a clear check for incompatible sizes.https://www.youtube-nocookie.com/embed/_oHixqtAKvc https://pythonlessonlab.com/lessons/pandas-pivot-table-multiple-aggregations/https://pythonlessonlab.com/assets/video-posters/pandas-pivot-table-multiple-aggregations.jpgPandas Pivot Table with Multiple AggregationsBuild a region-by-product pivot table with both sum and mean of an amount column, then read each measure reliably.https://www.youtube-nocookie.com/embed/VyVi6sz9dEw https://pythonlessonlab.com/lessons/pandas-fillna-different-columns/https://pythonlessonlab.com/assets/video-posters/pandas-fillna-different-columns.jpgPandas fillna: Different Values for Different ColumnsFill missing city and score values with separate defaults while leaving other columns and the input DataFrame unchanged.https://www.youtube-nocookie.com/embed/5PIo2k4bWPA https://pythonlessonlab.com/lessons/asyncio-gather-tasks-errors/https://pythonlessonlab.com/assets/video-posters/asyncio-gather-tasks-errors.jpgasyncio.gather: Run Tasks Together and Handle ErrorsRun independent coroutines together and turn returned exceptions into clear per-item results without losing input order.https://www.youtube-nocookie.com/embed/8heMSxOpO8E https://pythonlessonlab.com/lessons/pytest-parametrize-multiple-cases/https://pythonlessonlab.com/assets/video-posters/pytest-parametrize-multiple-cases.jpgpytest.mark.parametrize: Test Many Cases with One FunctionDesign a small table of input-output cases and run it as separate named pytest cases in a local project.https://www.youtube-nocookie.com/embed/wpYvZ-r-VvI https://pythonlessonlab.com/lessons/pandas-to-datetime-parse-dates/https://pythonlessonlab.com/assets/video-posters/pandas-to-datetime-parse-dates.jpgPandas to_datetime: Formats, Invalid Dates and errors='coerce'Convert date strings to UTC timestamps while identifying invalid or missing source values.https://www.youtube-nocookie.com/embed/1NUuGSjxzz0 https://pythonlessonlab.com/lessons/matplotlib-savefig-high-resolution/https://pythonlessonlab.com/assets/video-posters/matplotlib-savefig-high-resolution.jpgMatplotlib savefig: Sharp PNGs, DPI and TransparencySave the exact Figure you created to a PNG file at 200 DPI with labels inside the output.https://www.youtube-nocookie.com/embed/sA-loCP261c https://pythonlessonlab.com/lessons/python-re-findall-patterns/https://pythonlessonlab.com/assets/video-posters/python-re-findall-patterns.jpgPython re.findall: Extract Matches and Capture GroupsExtract complete ERR- and WARN- codes without returning only captured prefixes or partial codes.https://www.youtube-nocookie.com/embed/KaZhWCOkGlI https://pythonlessonlab.com/lessons/pydantic-field-validator-v2/https://pythonlessonlab.com/assets/video-posters/pydantic-field-validator-v2.jpgPydantic Field Validator: Validate and Normalize InputNormalize a handle before type validation while rejecting blank or non-string input.https://www.youtube-nocookie.com/embed/9Q-MfmDJZ1E https://pythonlessonlab.com/lessons/fastapi-query-parameters-pagination/https://pythonlessonlab.com/assets/video-posters/fastapi-query-parameters-pagination.jpgFastAPI Query Parameters: Defaults and ValidationAdd typed, bounded skip and limit query parameters to a GET route and apply them to a collection.https://www.youtube-nocookie.com/embed/Tpn8hyyYphU https://pythonlessonlab.com/lessons/pytest-tmp-path/https://pythonlessonlab.com/assets/video-posters/pytest-tmp-path.jpgpytest tmp_path: Test Code That Reads and Writes FilesUse pytest's tmp_path fixture to test a file writer in an isolated directory and assert the saved content.https://www.youtube-nocookie.com/embed/LOlfbFQpDG4 https://pythonlessonlab.com/lessons/dataclass-to-dict/https://pythonlessonlab.com/assets/video-posters/dataclass-to-dict.jpgDataclass to Dict with asdict() and Nested ValuesConvert dataclass instances to dictionaries with asdict and understand nested conversion versus shallow field access.https://www.youtube-nocookie.com/embed/KKPQw33sQ8I https://pythonlessonlab.com/lessons/jsonschema-validate-python/https://pythonlessonlab.com/assets/video-posters/jsonschema-validate-python.jpgValidate JSON Schema in Python and Explain ErrorsValidate Python data against a JSON Schema, collect errors, and distinguish a bad instance from a bad schema.https://www.youtube-nocookie.com/embed/lT8ryAyXHqU https://pythonlessonlab.com/lessons/python-csv-to-json/https://pythonlessonlab.com/assets/video-posters/python-csv-to-json.jpgCSV to JSON in Python: Headers, Types and EncodingTurn CSV rows into JSON objects with headers, UTF-8 text, and explicit handling for malformed rows.https://www.youtube-nocookie.com/embed/Jakwi6juC1c https://pythonlessonlab.com/lessons/numpy-boolean-indexing/https://pythonlessonlab.com/assets/video-posters/numpy-boolean-indexing.jpgNumPy Boolean Indexing with Multiple ConditionsBuild a Boolean mask, select matching NumPy values or rows, and distinguish a selected copy from assignment into the source.https://www.youtube-nocookie.com/embed/hbDFH6ZAJmo https://pythonlessonlab.com/problems/dictionary-changed-size-during-iteration/https://pythonlessonlab.com/assets/video-posters/dictionary-changed-size-during-iteration.jpgFix RuntimeError: dictionary changed size during iterationDeleting keys while looping over a dictionary invalidates its live iterator. Use a snapshot of keys for in-place deletion or build a new filtered dictionary, then verify the original-state rule.https://www.youtube-nocookie.com/embed/4oQeWfWA62M https://pythonlessonlab.com/problems/f-string-not-interpolating/https://pythonlessonlab.com/assets/video-posters/f-string-not-interpolating.jpgWhy Is My Python f-String Printing Curly Braces?Your output contains {name} instead of the value of name. Diagnose the missing f prefix, then learn when doubled braces are actually needed.https://www.youtube-nocookie.com/embed/Ub7CpWnLFrw https://pythonlessonlab.com/problems/filter-list-python/https://pythonlessonlab.com/assets/video-posters/filter-list-python.jpgFilter a Python List: Comprehension vs filter()Use a list comprehension when you need a list immediately. filter() applies a predicate lazily, so convert its iterator to a list only when you need the whole result.https://www.youtube-nocookie.com/embed/zvvdlr9zwkc https://pythonlessonlab.com/problems/fix-unboundlocalerror-python/https://pythonlessonlab.com/assets/video-posters/fix-unboundlocalerror-python.jpgFix UnboundLocalError in Python | Understand Local ScopeA function assigns to a name, so Python treats it as local throughout that function; reading it before a value is assigned raises UnboundLocalError. Pass the current value in and return the update, or initialize a branch-dependent local before reading it.https://www.youtube-nocookie.com/embed/F8M1izDEIJM https://pythonlessonlab.com/problems/isinstance-vs-type-python/https://pythonlessonlab.com/assets/video-posters/isinstance-vs-type-python.jpgPython isinstance() vs type(): Why a Subclass Check FailsUse isinstance(value, Base) when instances of Base and its subclasses are valid. Use an exact type check only when the contract intentionally excludes subclasses.https://www.youtube-nocookie.com/embed/ycmSrrtyvXY https://pythonlessonlab.com/problems/list-append-returns-none/https://pythonlessonlab.com/assets/video-posters/list-append-returns-none.jpgWhy Does Python list.append() Return None?The item was added, yet the variable assigned from append() contains None. See exactly which object changed and choose the right pattern for your program.https://www.youtube-nocookie.com/embed/_1zF0IOkhvI https://pythonlessonlab.com/problems/mutable-default-argument-retains-values/https://pythonlessonlab.com/assets/video-posters/mutable-default-argument-retains-values.jpgPython Mutable Default Arguments: Why Values PersistA default list is created when the function is defined, so later calls can reuse it. Trace that shared object, then create a fresh list when the caller omits the argument.https://www.youtube-nocookie.com/embed/kygQzZshAl8 https://pythonlessonlab.com/problems/naive-aware-datetime-typeerror/https://pythonlessonlab.com/assets/video-posters/naive-aware-datetime-typeerror.jpgFix Python's Naive and Aware Datetime TypeErrorA datetime without timezone information cannot be ordered against one with an offset. Identify what the naive value means, make that interpretation explicit, and verify comparisons across offsets.https://www.youtube-nocookie.com/embed/wBTGFpOPdC8 https://pythonlessonlab.com/problems/nonetype-object-not-subscriptable/https://pythonlessonlab.com/assets/video-posters/nonetype-object-not-subscriptable.jpgFix TypeError: 'NoneType' object is not subscriptableSquare brackets fail when the value before them is None. Trace the lookup that produced None, handle the missing record explicitly, and test the edge cases.https://www.youtube-nocookie.com/embed/kFThQzXf88E https://pythonlessonlab.com/problems/too-many-values-to-unpack-python/https://pythonlessonlab.com/assets/video-posters/too-many-values-to-unpack-python.jpgFix ValueError: too many values to unpack in PythonThe right-hand side produces more values than the assignment has targets. Count the fields, then choose the targets or a starred remainder that fits the data contract.https://www.youtube-nocookie.com/embed/W1v5U47tkSo https://pythonlessonlab.com/problems/unhashable-type-list-python/https://pythonlessonlab.com/assets/video-posters/unhashable-type-list-python.jpgFix TypeError: unhashable type: 'list' in PythonA list cannot be a set member or dictionary key because it is mutable and unhashable. Convert fixed coordinate values to tuples, then test duplicates and nested values.https://www.youtube-nocookie.com/embed/GGw6KZx3S6w https://pythonlessonlab.com/problems/valueerror-invalid-literal-int/https://pythonlessonlab.com/assets/video-posters/valueerror-invalid-literal-int.jpgFix ValueError: invalid literal for int() in Pythonint() can parse a valid whole-number string, but text such as '12.5' is not an integer literal. Inspect the actual input, validate the intended format, and test the edge cases.https://www.youtube-nocookie.com/embed/sIoEBGOamRk https://pythonlessonlab.com/problems/zero-division-error-python/https://pythonlessonlab.com/assets/video-posters/zero-division-error-python.jpgHow to Fix ZeroDivisionError in PythonDividing by zero stops a calculation. Trace where the divisor came from, decide what zero means for your program, and test that rule instead of hiding the error.https://www.youtube-nocookie.com/embed/3_XwKg58JnY https://pythonlessonlab.com/problems/input-returns-string-typeerror/https://pythonlessonlab.com/assets/video-posters/input-returns-string-typeerror.jpgWhy Does input() Cause a TypeError When Adding a Number?The characters a person types look like a number, but input() returns a string. Find the mismatched types, convert deliberately, and handle text that cannot be converted.https://www.youtube-nocookie.com/embed/_QPusCrvS5w https://pythonlessonlab.com/problems/modulenotfounderror-after-pip-install/https://pythonlessonlab.com/assets/video-posters/modulenotfounderror-after-pip-install.jpgModuleNotFoundError After pip install: Check the Python EnvironmentAn install can succeed in one Python environment while your program runs in another. Prove which interpreter each command uses, then make installation and execution use the same one.https://www.youtube-nocookie.com/embed/OqJgoE8B2qw https://pythonlessonlab.com/problems/loop-keeps-only-last-item/https://pythonlessonlab.com/assets/video-posters/loop-keeps-only-last-item.jpgWhy Does My Python Loop Keep Only the Last Item?If each loop iteration assigns a new value to one variable, the earlier values disappear. Trace the variable, create a collection before the loop, and add each result to it.https://www.youtube-nocookie.com/embed/LkLhacIzud4 https://pythonlessonlab.com/problems/filenotfounderror-existing-file/https://pythonlessonlab.com/assets/video-posters/filenotfounderror-existing-file.jpgFileNotFoundError When the File Exists: Check Your Working DirectoryA relative filename is resolved from the process working directory, which may differ from the script's folder. Print both paths, then choose an explicit location for the data file.https://www.youtube-nocookie.com/embed/QALZ83K52Vw https://pythonlessonlab.com/problems/list-index-out-of-range/https://pythonlessonlab.com/assets/video-posters/list-index-out-of-range.jpgHow to Fix IndexError: List Index Out of Range in PythonA list has fewer positions than your code expects. Reproduce the failure, inspect the list length, and choose a safe lookup or iteration pattern that matches the task.https://www.youtube-nocookie.com/embed/iS90ZBfhDWk https://pythonlessonlab.com/problems/function-prints-none/https://pythonlessonlab.com/assets/video-posters/function-prints-none.jpgWhy Does My Python Function Return None After Printing?A message on the screen is not a value returned to the caller. Trace the function's result, add an explicit return, and test how another line can use that value.https://www.youtube-nocookie.com/embed/Swbxq7RiPy0 https://pythonlessonlab.com/problems/dictionary-keyerror-missing-key/https://pythonlessonlab.com/assets/video-posters/dictionary-keyerror-missing-key.jpgHow to Fix KeyError for a Missing Python Dictionary KeyA dictionary lookup with square brackets requires the exact key to exist. Inspect the available keys, then decide whether a missing key should be handled or treated as an error.https://www.youtube-nocookie.com/embed/mmvGR9HCLwY https://pythonlessonlab.com/problems/sort-list-of-dicts-by-key/https://pythonlessonlab.com/assets/video-posters/sort-list-of-dicts-by-key.jpgSort a List of Dictionaries in Python | Fix TypeError with keysorted(products) cannot compare whole dictionaries. Reproduce the TypeError, select a numeric price key, and test ties without changing the original list.https://www.youtube-nocookie.com/embed/dCmAoC-4hgQ