Learn Python by typing · CodeTypeLearn

1Fundamentals0/30start →

Hello, world Variables and f-strings Booleans and None Constants by convention for over a range Define a function if / elif / else Integers never overflow Numeric types String basics Conditional expression while loop break and continue Chained comparisons List comprehension Default arguments Docstrings Loop with an index Read from stdin Keyword arguments Return multiple values Parse a number Truthiness Type hints Tuple unpacking for ... else Format numbers Match statement *args and **kwargs Walrus operator

2Strings In Depth0/19start →

Search a string Count occurrences Strings are immutable Index and slice Classify characters Iterate characters Case and trimming Repeat and pad Replace text split and join Iterate lines Capitalize and title case Zero-pad numbers Build a string str.format Split once with partition Strip a prefix or suffix str vs bytes Translate characters

3Values & References0/18start →

Names bind to objects Compare to None with is Aliasing Copy a list with [:]The id() of an object Immutable arguments are safe is vs ==Mutable vs immutable Tuples are immutable Shallow copy Immutable means hashable Pass-by-object-reference Rebinding a parameter is local Augmented assignment differs by type Deep copy Mutable default argument gotcha Shallow copy shares nested objects A tuple can hold a mutable object

4Slices & Arrays0/19Unlock →

Slice a range Count occurrences First and last Membership test Omit start or stop Copy via [:]Find an index Negative indices Reverse with a slice sorted returns a new list Step and stride Slice assignment Delete a slice Slice objects Sort in place with a key Binary search with bisect Fixed-size chunks Keep a list sorted Sliding windows

5Data structures0/20Unlock →

6Iterators0/20Unlock →

7Traits0/18Unlock →

__len____repr__Abstract base class Default method on an ABC __add____call____contains____eq____hash____neg____str__ vs __repr____getitem____iadd__Mixin class __mul__ by a scalar Protocol (structural typing)total_ordering __iter__ and __next__

8Generics0/18Unlock →

Typing containers Typing a callable Generic class Generic function Return T or None Generic returning a list Two type parameters Bounded TypeVar Constrained TypeVar Generic dataclass Generic over an iterable Generic with a key function Two-parameter generic class NewType typing.Self Generic Stack Protocol as a bound ParamSpec

9Lifetimes0/14Unlock →

del a name Comprehension scope global keyword LEGB scope contextlib.closing Closures keep objects alive Context manager contextmanager decorator The cyclic collector nonlocal keyword Reference counting Circular references Weak reference Weakref finalize callback

10Closures0/19Unlock →

A lambda Capturing the environment map and filter A small inline helper Callbacks Returning a function Capturing in a filter Higher-order function functools.partial functools.reduce reduce with an initial value A lambda as a sort key Currying nonlocal A list of functions A stateful closure Compose two functions A decorator Loop-variable capture gotcha

11Pattern Matching0/19Unlock →

Literals and wildcard Unpacking in assignment Capture a value Or-patterns Match a tuple's shape Unpacking in a for loop match as a value chooser Capture with as Match guards Ranges via a guard Mapping patterns Nested unpacking Sequence patterns Bind the ends, skip the middle Match on type Class patterns Capture the rest of a mapping Positional class patterns Nested patterns

12Error Handling0/19Unlock →

try / except assert an invariant Bind the exception Raise an exception Context in messages Custom exception class EAFP style try / except / else finally for cleanup Catch several types Read exception args Exception with attributes Cleanup with a context manager try / except / else / finally Exception hierarchy Ordered handlers Re-raise Emit a warning Chaining with raise from

13Option & Result0/18Unlock →

None means absence Guard against None dict.get with a default or for a fallback Optional type hint Conditional default Drop the Nones getattr with a default Transform only if present try/except as Result Require all present Chained lookups None as a default arg First truthy value next with a default contextlib.suppress Coalesce several options Walrus for optionals

14Conversions0/15Unlock →

Convert to float Convert to int Convert to str Convert to bool Numeric coercion Between sequence types Character and code point Number to base string bool is an int Build a dict format() a value Parse in another base Parse with error handling Text and bytes Safe literal parsing

15Collection Conversions0/18Unlock →

Keys to a list List to set List and tuple Set to sorted list Values to a list Frequency count Pairs to dict Zip into a dict Flatten nested lists Items to a list Sort a dict by key Flatten with chain Dedupe, keep order Group with defaultdict Invert a dict Set algebra to a list Runs with groupby Unzip pairs

16Math0/19Unlock →

Integer arithmetic min, max, clamp Math constants divmod Factorial Rounding Round to digits Roots and powers Sum and average GCD and LCM Logarithms and exp nan and infinity checks Trigonometry Combinations and permutations hypot and atan2 Comparing floats Integer square root Statistics module fmod and remainder

17Encoding0/21Unlock →

18Random0/20Unlock →

19Data I/O0/18Unlock →

Parse CSV rows Parse JSON Sum a column of numbers Tab-separated values Select one column CSV into a number matrix Write CSV CSV with a header Split off the header Pretty-print JSON JSON round-trip Whitespace-separated matrix Skip blanks and comments Print an aligned table CSV to a file and back Write CSV from dicts Parse key=value config Drop unparseable rows

20Linear Algebra0/22Unlock →

21Text Processing0/18Unlock →

Word count Capitalize and title case Count occurrences Replace text Reverse word order Strip whitespace Count vowels Zero-pad a number Pad and align Character frequency Longest word Number the lines Title case each word Most common words Wrap and shorten Truncate with an ellipsis String similarity Levenshtein distance

22Date & Time0/17Unlock →

Current date and time Date components Build a datetime Add days Difference between dates Seconds to H:M:S ISO 8601 format Format a datetime timedelta arithmetic Weekday and month names Parse a clock string Parse a datetime UNIX timestamp UTC-aware datetime Add months Convert between zones Real timezones

23Memory0/13Unlock →

Swap without a temp del and rebinding id() and identity is vs ==Shallow copy Deep copy sys.getsizeof gc.collect Small int caching Mutable default gotcha __slots__ saves memory String interning weakref.proxy

24Modules0/18Unlock →

from ... import Import a module The __main__ guard import ... as Inspect a module A module's docstring from ... import ... as Grouped import A module's __name__Standard-library tour Import a submodule Look up a name dynamically Namespaces avoid clashes Relative imports A module's namespace Control export with __all__Import by name Reload a module

25Macros0/21Unlock →

26Testing0/20Unlock →

27Algorithms0/12Unlock →

Reverse a string Greatest common divisor Palindrome check Binary search Fibonacci with memoization Pseudo-random numbers Memoize by hand Merge two sorted lists Two sum Partition around a pivot Quicksort Fisher-Yates shuffle

28Sorting Algorithms0/13Unlock →

Check if sorted sorted vs list.sort Bubble sort Heapsort with heapq Insertion sort Sort by key and reverse Selection sort Counting sort Merge sort Shell sort Heapsort by hand Quicksort in place Radix sort

29Expression Parsing0/6Unlock →

Evaluate postfix (RPN)Tokenize an expression Evaluate infix Recursive-descent calculator Right-associative power Shunting-yard

30Idioms0/15Unlock →

Chained comparisons dict.get default f-strings Conditional expression Truthiness checks Underscore for unused any and all Comprehensions over loops enumerate and zip join over concatenation sorted with a key Unpacking EAFP over LBYL Generator expressions Context managers

31OOP & Traits0/14Unlock →

Class and __init__Methods that mutate state Inheritance Instance vs class attributes Method override @staticmethod super()@classmethod Composition Encapsulation Polymorphism (duck typing)@property Property setter __slots__

32Trait Objects0/12Unlock →

A list of mixed objects Dispatch by capability Dispatch with isinstance An ABC-typed collection A pipeline of callables Return one of several types Resolve a method by name Protocol-typed parameter A function registry runtime_checkable Protocol functools.singledispatch singledispatchmethod

33Design Patterns0/14Unlock →

Singleton Adapter Builder Factory Method Lazy Initialization Observer Prototype Strategy Command Decorator State Dependency Injection Object Pool Actor

34Async0/11Unlock →

async def and await create_task Run coroutines concurrently Async generator run_until_complete asyncio.Queue Concurrent vs sequential asyncio.to_thread wait_for with a timeout as_completed An async iterator

35File I/O0/10Unlock →

Read a whole file Read lines Write a file Write many lines Append to a file pathlib read/write text Round-trip via a temp file Read in chunks Write and read CSV Write and read JSON

36Filesystem0/20Unlock →

37Networking0/16Unlock →

Resolve a hostname Parse an HTTP request line Route by path Parse and validate an address Build a query string Parse a URL Bind an ephemeral port Build an HTTP response Receive until closed Shut down a connection A TCP listening socket Socket timeout UDP send and receive Prepare an HTTP request http.server request handler TCP client and server

38Concurrency0/15Unlock →

The GIL, in short Spawn a thread Pass arguments to a thread Daemon threads Event as a stop flag ThreadPoolExecutor.map Barrier Shared state with a Lock submit and Future Producer/consumer with a Queue RLock (re-entrant lock)Semaphore Condition variable threading.local multiprocessing.Pool

39Unsafe & FFI0/14Unlock →

Mutate a bytearray sys.getsizeof id() as an address The array module int <-> bytes A writable C buffer Call a C library function Share memory with a view memoryview struct.pack and unpack Pointers with byref ctypes.cast A ctypes Structure Reinterpret float bits

40Commands0/15Unlock →

Just the user's args Command-line arguments Current directory Env var with a default Read an environment variable Iterate all env vars Set and remove a variable Exit with a code Path to this file Find a program on PATH Parse args with argparse Command exit status Run a command Pass env to a child Read all of stdin

41Array0/10Unlock →

Contains Duplicate Best Time to Buy and Sell Stock Two Sum Container With Most Water Maximum Subarray Find Minimum in Rotated Sorted Array Maximum Product Subarray Product of Array Except Self Search in Rotated Sorted Array 3Sum

42Binary0/5Unlock →

Missing Number Number of 1 Bits Counting Bits Reverse Bits Sum of Two Integers

43String0/10Unlock →

Valid Anagram Valid Palindrome Valid Parentheses Group Anagrams Palindromic Substrings Encode and Decode Strings Longest Palindromic Substring Longest Substring Without Repeating Characters Longest Repeating Character Replacement Minimum Window Substring

44Matrix0/4Unlock →

Set Matrix Zeroes Rotate Image Spiral Matrix Word Search

45Interval0/5Unlock →

Meeting Rooms Merge Intervals Insert Interval Non-overlapping Intervals Meeting Rooms II

46Linked List0/6Unlock →

Reverse Linked List Linked List Cycle Merge Two Sorted Lists Remove Nth Node From End Merge K Sorted Lists Reorder List

47Tree0/14Unlock →

Invert Binary Tree Maximum Depth of Binary Tree Same Tree Lowest Common Ancestor of a BST Binary Tree Level Order Traversal Subtree of Another Tree Kth Smallest Element in a BST Implement Trie (Prefix Tree)Validate Binary Search Tree Add and Search Word Construct Binary Tree from Preorder and Inorder Binary Tree Maximum Path Sum Serialize and Deserialize Binary Tree Word Search II

48Graph0/8Unlock →

Clone Graph Number of Connected Components Course Schedule Longest Consecutive Sequence Number of Islands Graph Valid Tree Pacific Atlantic Water Flow Alien Dictionary

49Heap0/3Unlock →

Kth Largest Element in an Array Top K Frequent Elements Find Median from Data Stream

50Dynamic Programming0/11Unlock →

Climbing Stairs House Robber Jump Game Unique Paths Coin Change Combination Sum IV Decode Ways House Robber II Word Break Longest Common Subsequence Longest Increasing Subsequence