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Python
Mutability, comprehensions, generators, decorators, classes and the standard library: what Python-heavy teams test.
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Visual, hands-on lessons for every pattern in this topic. Do the lesson, then come back and the questions click.
100 questions, most asked first
Ranked by how often each question comes up in real interviews. #1 is the most common.
All patternsData types & mutabilityPythonic codeDecorators & context managersIterators & generatorsFunctionsConcurrencyStandard libraryErrorsOOP & dunder methods
#1💬The mutable default argument trapData types & mutabilityMediumFree#2💬List vs tupleData types & mutabilityEasyFree#3💬is vs ==Data types & mutabilityEasyFree#4💬Mutable vs immutable types and referencesData types & mutabilityMediumFree#5⌨️List comprehensionsPythonic codeEasyFree#6⌨️Write a decoratorDecorators & context managersMediumFree#7⌨️Generators and yieldIterators & generatorsMediumFree#8💬*args and **kwargsFunctionsEasyFree#9💬How do dicts and sets work?Data types & mutabilityMediumFree#10💬Shallow copy vs deep copyData types & mutabilityMediumFree🔓Unlock 90 more Python questions · all 1,200 questions for $39/year (about 11¢ a day)See full access#11💬What is the GIL?ConcurrencyMedium🔒#12⌨️Count word frequencyStandard libraryEasy🔒#13💬try / except / else / finallyErrorsEasy🔒#14⌨️Context managers and withDecorators & context managersMedium🔒#15⌨️Dunder (magic) methodsOOP & dunder methodsMedium🔒#16💬__init__ vs __new__OOP & dunder methodsHard🔒#17💬classmethod vs staticmethodOOP & dunder methodsMedium🔒#18💬Inheritance, super() and the MROOOP & dunder methodsHard🔒#19⌨️lambda, map, filter and sorted with keyFunctionsEasy🔒#20💬SlicingPythonic codeEasy🔒#21⌨️enumerate and zipPythonic codeEasy🔒#22⌨️dict.get, setdefault and defaultdictStandard libraryEasy🔒#23💬dataclasses and namedtuplesOOP & dunder methodsMedium🔒#24💬Scope rules (LEGB), global and nonlocalFunctionsMedium🔒#25💬Late-binding closures in loopsFunctionsHard🔒#26⌨️Build an iterator classIterators & generatorsMedium🔒#27💬Threading vs multiprocessing vs asyncioConcurrencyMedium🔒#28💬async and await in PythonConcurrencyMedium🔒#29💬f-strings and string formattingPythonic codeEasy🔒#30💬Integer division and modulo with negativesData types & mutabilityMedium🔒#31💬Truthiness in PythonData types & mutabilityEasy🔒#32💬Checking for NoneData types & mutabilityEasy🔒#33💬The walrus operator (:=)Pythonic codeEasy🔒#34💬Unpacking and star expressionsPythonic codeEasy🔒#35⌨️Invert a dictionary (dict comprehension)Pythonic codeEasy🔒#36⌨️Set operationsData types & mutabilityEasy🔒#37⌨️Flatten a nested list (recursion + generators)Iterators & generatorsMedium🔒#38⌨️Memoization with functools.lru_cacheDecorators & context managersEasy🔒#39⌨️@property: getters and settersOOP & dunder methodsMedium🔒#40💬__slots__OOP & dunder methodsHard🔒#41💬Abstract base classesOOP & dunder methodsMedium🔒#42💬Duck typing and EAFPOOP & dunder methodsEasy🔒#43💬Type hints in PythonFunctionsEasy🔒#44💬Virtual environments and dependenciesStandard libraryEasy🔒#45💬if __name__ == "__main__"Standard libraryEasy🔒#46⌨️Working with JSONStandard libraryEasy🔒#47💬Dates and time zonesStandard libraryMedium🔒#48⌨️Regular expressions with reStandard libraryMedium🔒#49⌨️itertools in practiceStandard libraryMedium🔒#50⌨️heapq for top-k and schedulingStandard libraryMedium🔒#51⌨️Binary search with bisectStandard libraryMedium🔒#52⌨️deque for queues and sliding windowsStandard libraryMedium🔒#53💬Why use join to build strings?Pythonic codeMedium🔒#54💬append vs extend vs +Data types & mutabilityEasy🔒#55💬list.sort() vs sorted()Pythonic codeEasy🔒#56💬Chained comparisonsPythonic codeEasy🔒#57⌨️any() and all()Pythonic codeEasy🔒#58⌨️Custom exceptionsErrorsMedium🔒#59💬Exception chaining with raise fromErrorsMedium🔒#60💬logging vs printStandard libraryEasy🔒#61💬Testing with pytestFunctionsEasy🔒#62💬Memory management in PythonData types & mutabilityMedium🔒#63💬Why does `is` work for small numbers?Data types & mutabilityMedium🔒#64💬What does range() actually return?Iterators & generatorsEasy🔒#65💬Generator expressions vs list comprehensionsIterators & generatorsMedium🔒#66💬DescriptorsOOP & dunder methodsHard🔒#67💬MetaclassesOOP & dunder methodsHard🔒#68💬__eq__ and __hash__ togetherOOP & dunder methodsHard🔒#69⌨️Making objects sortableOOP & dunder methodsMedium🔒#70💬__str__ vs __repr__OOP & dunder methodsEasy🔒#71⌨️functools.partialFunctionsEasy🔒#72⌨️functools.reduceFunctionsEasy🔒#73💬map/filter vs comprehensionsPythonic codeEasy🔒#74⌨️zip vs zip_longestStandard libraryEasy🔒#75💬The for…else clausePythonic codeMedium🔒#76💬return inside finallyErrorsHard🔒#77💬Python integers never overflowData types & mutabilityEasy🔒#78💬Floats vs Decimal for moneyStandard libraryMedium🔒#79💬str vs bytes and encodingsData types & mutabilityMedium🔒#80⌨️Sorting by multiple keysPythonic codeMedium🔒#81💬Class attributes vs instance attributesOOP & dunder methodsMedium🔒#82💬Private attributes and name manglingOOP & dunder methodsMedium🔒#83⌨️EnumsStandard libraryEasy🔒#84💬Race conditions and locks in PythonConcurrencyMedium🔒#85💬Flask vs Django vs FastAPIStandard libraryEasy🔒#86💬WSGI vs ASGIConcurrencyMedium🔒#87💬PEP 8 and clean PythonPythonic codeEasy🔒#88💬Finding slow Python codeStandard libraryMedium🔒#89💬Why is NumPy fast?Standard libraryMedium🔒#90💬Time complexity of Python built-insData types & mutabilityMedium🔒#91💬break, continue and passPythonic codeEasy🔒#92⌨️String cleanup — make a URL slugPythonic codeEasy🔒#93💬Are dictionaries ordered?Data types & mutabilityEasy🔒#94⌨️Transpose a matrix with zipPythonic codeEasy🔒#95⌨️A decorator that takes argumentsDecorators & context managersHard🔒#96💬When to use assertErrorsMedium🔒#97⌨️Reading a file line by lineDecorators & context managersEasy🔒#98💬Is Python compiled or interpreted?FunctionsMedium🔒#99💬Structural pattern matching (match/case)Pythonic codeMedium🔒#100⌨️Closures in PythonFunctionsEasy🔒