## Table 1: Data Types | **Type** | **Example** | **Description** | |---|---|---| | [**int**](https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex) | `x = 42` | • **Arbitrary-precision integers**
• no overflow limit unlike many languages. | | [**float**](https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex) | `y = 3.14` | • Double-precision floating-point numbers (64-bit IEEE 754)
• **beware rounding errors**. | | [**complex**](https://docs.python.org/3/library/stdtypes.html#numeric-types-int-float-complex) | `z = 1 + 2j` | • **Numbers with real and imaginary parts**
• `j` suffix denotes imaginary unit. | | [**str**](https://docs.python.org/3/library/stdtypes.html#text-sequence-type-str) | `s = "hello"` | • Immutable sequence of Unicode characters
• supports **f-strings, slicing, and rich methods**. | | [**bool**](https://docs.python.org/3/library/stdtypes.html#boolean-type-bool) | `flag = True` | **Subclass of `int`** with values `True` (1) or `False` (0). | | [**list**](https://docs.python.org/3/library/stdtypes.html#list) | `arr = [1, 2, 3]` | • Mutable ordered sequence
• **most versatile** collection type. | | [**tuple**](https://docs.python.org/3/library/stdtypes.html#tuple) | `t = (1, 2, 3)` | • Immutable ordered sequence
• **hashable** when elements are hashable, useful as dict keys. | | [**dict**](https://docs.python.org/3/library/stdtypes.html#mapping-types-dict) | `d = {"key": "val"}` | • Mutable mapping of **unique keys** to values
• insertion-ordered since Python 3.7. | | [**set**](https://docs.python.org/3/library/stdtypes.html#set-types-set-frozenset) | `s = {1, 2, 3}` | • Mutable unordered collection of **unique hashable** elements
• supports set operations. | | [**frozenset**](https://docs.python.org/3/library/stdtypes.html#set-types-set-frozenset) | `fs = frozenset([1, 2])` | • Immutable version of `set`
• **hashable**, can be dict key or set element. | | [**None**](https://docs.python.org/3/library/stdtypes.html#the-null-object) | `x = None` | • Singleton representing **absence of value**
• distinct from empty collections or zero. | | [**bytes**](https://docs.python.org/3/library/stdtypes.html#bytes-objects) | `b = b"data"` | • Immutable sequence of **byte values** (0-255)
• for binary data. | | [**bytearray**](https://docs.python.org/3/library/stdtypes.html#bytearray-objects) | `ba = bytearray(b"x")` | • **Mutable version of `bytes`**
• in-place modification of binary data. | | [**range**](https://docs.python.org/3/library/stdtypes.html#ranges) | `r = range(10)` | • Immutable sequence representing an **arithmetic progression**
• memory-efficient for iteration. | ## Table 2: Operators | **Operator** | **Example** | **Description** | |---|---|---| | [**Arithmetic**](https://docs.python.org/3/library/operator.html) | `x + y`, `x - y`, `x * y` | • **Addition, subtraction, multiplication**
• work on numbers and some sequences. | | [**Division**](https://docs.python.org/3/library/operator.html#operator.truediv) | `x / y` | • True division
• **always returns float** even for integer operands. | | [**Floor division**](https://docs.python.org/3/library/operator.html#operator.floordiv) | `x // y` | • Division rounded **down to nearest integer**
• result type depends on operands. | | [**Modulo**](https://docs.python.org/3/library/operator.html#operator.mod) | `x % y` | • Remainder of division
• **sign matches divisor** unlike some languages. | | [**Exponentiation**](https://docs.python.org/3/library/operator.html#operator.pow) | `x ** y` | • **Raises `x` to power `y`**
• supports negative and fractional exponents. | | [**Comparison**](https://docs.python.org/3/library/stdtypes.html#comparisons) | `x == y`, `x != y`, `x < y` | • Equality, inequality, less-than
• **chainable** like `x < y < z`. | | [**Identity**](https://docs.python.org/3/reference/expressions.html#is) | `x is y` | • Tests if objects are **same instance**
• not value equality. | | [**Membership**](https://docs.python.org/3/reference/expressions.html#membership-test-operations) | `x in y` | • **Checks if `x` exists** in container `y`
• efficient for sets/dicts. | | [**Logical AND**](https://docs.python.org/3/library/stdtypes.html#boolean-operations-and-or-not) | `x and y` | • Returns first **falsy value** or last value if all truthy
• **short-circuits**. | | [**Logical OR**](https://docs.python.org/3/library/stdtypes.html#boolean-operations-and-or-not) | `x or y` | • Returns first **truthy value** or last value if all falsy
• short-circuits. | | [**Logical NOT**](https://docs.python.org/3/library/stdtypes.html#boolean-operations-and-or-not) | `not x` | • **Boolean negation**
• returns `True` if `x` is falsy. | | [**Bitwise AND**](https://docs.python.org/3/library/operator.html#operator.and_) | `x & y` | • Bitwise AND of integers
• also **set intersection** for sets. | | [**Bitwise OR**](https://docs.python.org/3/library/operator.html#operator.or_) | x | y | • Bitwise OR of integers
• also **set union** for sets. | | [**Bitwise XOR**](https://docs.python.org/3/library/operator.html#operator.xor) | `x ^ y` | • Bitwise exclusive OR
• also **symmetric difference** for sets. | | [**Bitwise NOT**](https://docs.python.org/3/library/operator.html#operator.inv) | `~x` | • **One's complement**
• inverts all bits. | | [**Left shift**](https://docs.python.org/3/library/operator.html#operator.lshift) | `x << n` | • Shifts bits left by `n` positions
• equivalent to multiplying by `2**n`. | | [**Right shift**](https://docs.python.org/3/library/operator.html#operator.rshift) | `x >> n` | • Shifts bits right by `n` positions
• equivalent to floor dividing by `2**n`. | | [**Dict merge operator**](https://peps.python.org/pep-0584/) | d1 | d2 | • Merges two dicts into **new dict**
• |= updates in-place (Python 3.9+). | | [**Walrus operator**](https://peps.python.org/pep-0572/) | `(x := 5)` | • Assignment expression
• **assigns and returns** value in single operation (Python 3.8+). | ## Table 3: String Operations | **Method** | **Example** | **Description** | |---|---|---| | [**f-strings**](https://docs.python.org/3/reference/lexical_analysis.html#f-strings) | `f"{x} + {y} = {x+y}"` | • Formatted string literals
• **fastest and most readable** formatting method
• nested quotes and multiline expressions since 3.12. | | [**format()**](https://docs.python.org/3/library/string.html#formatstrings) | `"{} {}".format(a, b)` | • **String formatting** with positional/keyword arguments
• more verbose than f-strings. | | [**split()**](https://docs.python.org/3/library/stdtypes.html#str.split) | `s.split(",")` | • Splits string into list by delimiter
• **default splits on whitespace**. | | [**join()**](https://docs.python.org/3/library/stdtypes.html#str.join) | `",".join(items)` | • Concatenates iterable into single string with separator
• **preferred over +=** in loops. | | [**strip()**](https://docs.python.org/3/library/stdtypes.html#str.strip) | `s.strip()` | • Removes **leading and trailing** whitespace
• `lstrip()`/`rstrip()` for one side. | | [**removeprefix() / removesuffix()**](https://docs.python.org/3/library/stdtypes.html#str.removeprefix) | `s.removeprefix("pre")` | • Removes exact **prefix or suffix** if present
• returns unchanged string otherwise (Python 3.9+). | | [**replace()**](https://docs.python.org/3/library/stdtypes.html#str.replace) | `s.replace("old", "new")` | • **Returns copy** with all occurrences replaced
• optional count parameter. | | [**upper() / lower()**](https://docs.python.org/3/library/stdtypes.html#str.upper) | `s.upper()` | • Case conversion
• `casefold()` for **aggressive case-insensitive** comparisons. | | [**startswith() / endswith()**](https://docs.python.org/3/library/stdtypes.html#str.startswith) | `s.startswith("pre")` | • **Checks if string starts/ends** with prefix/suffix
• accepts tuple of options. | | [**find() / index()**](https://docs.python.org/3/library/stdtypes.html#str.find) | `s.find("sub")` | • Searches substring position
• `find()` returns **-1 if not found**, `index()` raises exception. | | [**isdigit() / isalpha()**](https://docs.python.org/3/library/stdtypes.html#str.isdigit) | `s.isdigit()` | • **Character type checks**
• many variants like `isalnum()`, `isspace()`. | | [**t-strings**](https://peps.python.org/pep-0750/) | `t"Hello {name}"` | • Template strings producing **`Template` object** for custom processing
• generalization of f-strings (Python 3.14+). | | [**%-formatting (legacy)**](https://docs.python.org/3/library/stdtypes.html#old-string-formatting) | `"%s %d" % (s, n)` | • C-style formatting
• **replaced by f-strings** but still commonly seen in older code. | ## Table 4: Slicing and Indexing | **Pattern** | **Example** | **Description** | |---|---|---| | [**Positive indexing**](https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-range) | `s[0]`, `s[2]` | • **Zero-based indexing** from start
• first element is `[0]`. | | [**Negative indexing**](https://docs.python.org/3/library/stdtypes.html#sequence-types-list-tuple-range) | `s[-1]`, `s[-2]` | • Indexes from end
• **-1 is last element**, -2 second-to-last. | | [**Basic slice**](https://docs.python.org/3/library/functions.html#slice) | `s[1:4]` | Elements from index 1 up to (but **not including**) 4. | | [**Omit start**](https://docs.python.org/3/library/functions.html#slice) | `s[:3]` | • **From beginning** to index 3
• equivalent to `s[0:3]`. | | [**Omit end**](https://docs.python.org/3/library/functions.html#slice) | `s[2:]` | • **From index 2 to end**
• includes last element. | | [**Full copy**](https://docs.python.org/3/library/functions.html#slice) | `s[:]` | Creates **shallow copy** of entire sequence. | | [**Step slicing**](https://docs.python.org/3/library/functions.html#slice) | `s[::2]` | • Every 2nd element
• third parameter is **step size**. | | [**Reverse**](https://docs.python.org/3/library/functions.html#slice) | `s[::-1]` | • Reverses sequence
• **negative step** iterates backward. | | [**Negative step slice**](https://docs.python.org/3/library/functions.html#slice) | `s[4:1:-1]` | From index 4 down to (but **not including**) 1. | ## Table 5: Control Flow | **Statement** | **Example** | **Description** | |---|---|---| | [**if**](https://docs.python.org/3/tutorial/controlflow.html#if-statements) | `if x > 0:`
` print("pos")` | • Conditional execution
• tests **truthiness** of expression. | | [**elif**](https://docs.python.org/3/tutorial/controlflow.html#if-statements) | `elif x == 0:`
` print("zero")` | • Chain multiple conditions
• only **first true** branch executes. | | [**else**](https://docs.python.org/3/tutorial/controlflow.html#if-statements) | `else:`
` print("neg")` | **Executes when all if/elif conditions are false.** | | [**Ternary expression**](https://docs.python.org/3/reference/expressions.html#conditional-expressions) | `x if cond else y` | • Inline conditional
• returns `x` if **cond is true**, else `y`. | | [**for loop**](https://docs.python.org/3/tutorial/controlflow.html#for-statements) | `for i in range(5):`
` print(i)` | • Iterates over any **iterable object**
• most common loop type. | | [**while loop**](https://docs.python.org/3/reference/compound_stmts.html#while) | `while x > 0:`
` x -= 1` | • Repeats while condition is **truthy**
• check happens before each iteration. | | [**break**](https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops) | `break` | Exits **innermost** enclosing loop immediately. | | [**continue**](https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops) | `continue` | Skips to **next iteration** of innermost loop. | | [**else on loops**](https://docs.python.org/3/tutorial/controlflow.html#break-and-continue-statements-and-else-clauses-on-loops) | `for i in items:`
` pass`
`else:`
` print("done")` | • Executes if loop completes **without break**
• useful for search patterns. | | [**pass**](https://docs.python.org/3/reference/simple_stmts.html#pass) | `pass` | • Null operation
• **syntactic placeholder** where statement required. | | [**match-case**](https://peps.python.org/pep-0636/) | `match x:`
` case 1:`
` print("one")` | • Structural pattern matching with **guards, captures, and destructuring**
• switch-like statement (Python 3.10+). | ## Table 6: Functions | **Technique** | **Example** | **Description** | |---|---|---| | [**Function definition**](https://docs.python.org/3/tutorial/controlflow.html#defining-functions) | `def func(a, b):`
` return a + b` | • Creates reusable code block
• **`return` without value** returns `None`. | | [**Default arguments**](https://docs.python.org/3/tutorial/controlflow.html#default-argument-values) | `def f(x, y=10):` | • Parameters with **default values**
• must come after required params. | | [**Keyword arguments**](https://docs.python.org/3/tutorial/controlflow.html#keyword-arguments) | `f(x=1, y=2)` | • Named parameters
• allows **any order** and improves clarity. | | [***args**](https://docs.python.org/3/tutorial/controlflow.html#arbitrary-argument-lists) | `def f(*args):` | • Variable positional arguments
• collected as **tuple**. | | [****kwargs**](https://docs.python.org/3/tutorial/controlflow.html#arbitrary-argument-lists) | `def f(**kwargs):` | • Variable keyword arguments
• collected as **dict**. | | [**Lambda**](https://docs.python.org/3/tutorial/controlflow.html#lambda-expressions) | `lambda x: x * 2` | • Anonymous function
• **single expression** only, no statements. | | [**Docstring**](https://peps.python.org/pep-0257/) | `"""Description""" ` | • First string in function
• **accessible via `__doc__`**
• used by help(). | | [**Type hints**](https://docs.python.org/3/library/typing.html) | `def f(x: int) -> int:` | • Optional annotations
• **not enforced** at runtime but used by type checkers. | | [**Unpacking in calls**](https://docs.python.org/3/tutorial/controlflow.html#unpacking-argument-lists) | `f(*args, **kwargs)` | **Expands sequences and mappings** into function arguments. | ## Table 7: Comprehensions and Generators | **Technique** | **Example** | **Description** | |---|---|---| | [**List comprehension**](https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions) | `[x**2 for x in range(10)]` | • Creates list from iterable
• **faster and cleaner** than for-loop append. | | [**With condition**](https://docs.python.org/3/tutorial/datastructures.html#list-comprehensions) | `[x for x in nums if x > 0]` | • Filters elements
• condition acts as **inline filter**. | | [**Nested comprehension**](https://docs.python.org/3/tutorial/datastructures.html#nested-list-comprehensions) | `[x+y for x in a for y in b]` | • Multiple `for` clauses
• **left-to-right** nesting order. | | [**Dict comprehension**](https://docs.python.org/3/tutorial/datastructures.html#dictionaries) | `{k: v**2 for k, v in d.items()}` | • Creates dict from iterable
• key-value pairs with **unique keys**. | | [**Set comprehension**](https://docs.python.org/3/tutorial/datastructures.html#sets) | `{x**2 for x in nums}` | • Creates set
• **automatically deduplicates** results. | | [**Generator expression**](https://docs.python.org/3/reference/expressions.html#generator-expressions) | `(x**2 for x in range(10))` | • Lazy evaluation
• **memory-efficient** for large sequences. | | [**Generator function**](https://docs.python.org/3/tutorial/classes.html#generators) | `def gen():`
` yield x` | • Function with `yield`
• **pauses and resumes** execution on each call. | | [**yield from**](https://peps.python.org/pep-0380/) | `yield from iterable` | • Delegates to subiterator
• **simplifies nested generators** (Python 3.3+). | ## Table 8: Classes and OOP | **Concept** | **Example** | **Description** | |---|---|---| | [**Class definition**](https://docs.python.org/3/tutorial/classes.html#class-definition-syntax) | `class Dog:`
` pass` | • Creates new type
• **naming convention is PascalCase**. | | [**__init__**](https://docs.python.org/3/reference/datamodel.html#object.__init__) | `def __init__(self, name):` | • Constructor
• **initializes instance** when object created. | | [**Instance attributes**](https://docs.python.org/3/tutorial/classes.html#instance-objects) | `self.name = name` | • Per-object data
• **defined in `__init__`** or other methods. | | [**Class attributes**](https://docs.python.org/3/tutorial/classes.html#class-and-instance-variables) | `class Dog:`
` species = "Canis"` | • Shared across all instances
• **defined at class level**. | | [**Methods**](https://docs.python.org/3/tutorial/classes.html#method-objects) | `def bark(self):` | • Functions bound to instance
• **first param is `self`** by convention. | | [**Inheritance**](https://docs.python.org/3/tutorial/classes.html#inheritance) | `class Puppy(Dog):` | • Derives from parent class
• inherits **attributes and methods**. | | [**super()**](https://docs.python.org/3/library/functions.html#super) | `super().__init__(name)` | • Calls parent class method
• handles **multiple inheritance** correctly. | | [**@property**](https://docs.python.org/3/library/functions.html#property) | `@property`
`def age(self):` | • Getter method
• **accessed like attribute** but computed dynamically. | | [**@property.setter**](https://docs.python.org/3/library/functions.html#property) | `@age.setter`
`def age(self, val):` | • Setter method
• allows **validation and side effects** on assignment. | | [**@classmethod**](https://docs.python.org/3/library/functions.html#classmethod) | `@classmethod`
`def factory(cls):` | • Method receives **class not instance**
• for alternative constructors. | | [**@staticmethod**](https://docs.python.org/3/library/functions.html#staticmethod) | `@staticmethod`
`def util():` | • Regular function in class namespace
• **no implicit first parameter**. | | [**Multiple inheritance**](https://docs.python.org/3/tutorial/classes.html#multiple-inheritance) | `class C(A, B):` | • Inherits from multiple classes
• uses **MRO** (Method Resolution Order). | | [**__str__ / __repr__**](https://docs.python.org/3/reference/datamodel.html#object.__repr__) | `def __repr__(self):` | • String representations
• **`__repr__` for debugging**, `__str__` for users. | | [**__slots__**](https://docs.python.org/3/reference/datamodel.html#slots) | `__slots__ = ('x', 'y')` | • Declares fixed attributes
• **reduces memory** and prevents `__dict__` creation. | | [**__init_subclass__**](https://docs.python.org/3/reference/datamodel.html#object.__init_subclass__) | `def __init_subclass__(cls):` | • Hook called when class is subclassed
• **modern alternative to metaclasses** (Python 3.6+). | ## Table 9: Magic Methods (Dunder Methods) | **Method** | **Example** | **Description** | |---|---|---| | [**__init__**](https://docs.python.org/3/reference/datamodel.html#object.__init__) | `def __init__(self):` | • Instance initialization
• called when **object is created**. | | [**__str__**](https://docs.python.org/3/reference/datamodel.html#object.__str__) | `def __str__(self):` | • **Informal string representation**
• used by `str()` and `print()`. | | [**__repr__**](https://docs.python.org/3/reference/datamodel.html#object.__repr__) | `def __repr__(self):` | • Official string representation
• **should be valid Python** when possible. | | [**__len__**](https://docs.python.org/3/reference/datamodel.html#object.__len__) | `def __len__(self):` | • Returns length
• called by `len()`
• **must return non-negative int**. | | [**__getitem__**](https://docs.python.org/3/reference/datamodel.html#object.__getitem__) | `def __getitem__(self, key):` | • Indexing operator `[]`
• enables **subscript access**. | | [**__setitem__**](https://docs.python.org/3/reference/datamodel.html#object.__setitem__) | `def __setitem__(self, k, v):` | • Item assignment `[k] = v`
• makes object **mutable container**. | | [**__iter__**](https://docs.python.org/3/reference/datamodel.html#object.__iter__) | `def __iter__(self):` | • Returns iterator
• enables **for-loop support**. | | [**__next__**](https://docs.python.org/3/library/stdtypes.html#iterator.__next__) | `def __next__(self):` | • Gets next value
• raises **`StopIteration`** when exhausted. | | [**__enter__ / __exit__**](https://docs.python.org/3/reference/datamodel.html#context-managers) | `def __enter__(self):` | • Context manager protocol
• **enables `with` statement**. | | [**__add__**](https://docs.python.org/3/reference/datamodel.html#object.__add__) | `def __add__(self, other):` | • Addition operator `+`
• **return new object**, don't modify self. | | [**__eq__**](https://docs.python.org/3/reference/datamodel.html#object.__eq__) | `def __eq__(self, other):` | • Equality operator `==`
• **default compares identity**. | | [**__lt__ / __gt__**](https://docs.python.org/3/reference/datamodel.html#object.__lt__) | `def __lt__(self, other):` | • Comparison operators `<` and `>`
• enables **sorting**. | | [**__call__**](https://docs.python.org/3/reference/datamodel.html#object.__call__) | `def __call__(self):` | • Makes instance callable like function
• **enables `obj()` syntax**. | | [**__contains__**](https://docs.python.org/3/reference/datamodel.html#object.__contains__) | `def __contains__(self, item):` | • Membership test `in`
• should return **boolean**. | ## Table 10: Exception Handling | **Technique** | **Example** | **Description** | |---|---|---| | [**try-except**](https://docs.python.org/3/tutorial/errors.html#handling-exceptions) | `try:`
` risky()`
`except ValueError:` | • Catches exceptions
• **specific types** should precede general. | | [**Multiple exceptions**](https://docs.python.org/3/tutorial/errors.html#handling-exceptions) | `except (ValueError, KeyError):` | • Catches multiple types
• **tuple of exception classes**. | | [**except with variable**](https://docs.python.org/3/tutorial/errors.html#handling-exceptions) | `except ValueError as e:` | • Captures exception object
• **access message and details**. | | [**else clause**](https://docs.python.org/3/tutorial/errors.html#handling-exceptions) | `else:`
` print("success")` | • Runs if **no exception raised**
• before `finally`. | | [**finally**](https://docs.python.org/3/tutorial/errors.html#defining-clean-up-actions) | `finally:`
` cleanup()` | • Always executes
• **even if exception or return**
• for resource cleanup. | | [**raise**](https://docs.python.org/3/tutorial/errors.html#raising-exceptions) | `raise ValueError("msg")` | • Throws exception
• can **re-raise** caught exception with bare `raise`. | | [**Custom exceptions**](https://docs.python.org/3/tutorial/errors.html#user-defined-exceptions) | `class MyError(Exception):` | • Define new exception types
• **inherit from Exception or subclass**. | | [**Exception chaining**](https://docs.python.org/3/tutorial/errors.html#exception-chaining) | `raise NewError() from e` | • Links exceptions
• **preserves original cause** for debugging. | | [**ExceptionGroup**](https://docs.python.org/3/library/exceptions.html#ExceptionGroup) | `raise ExceptionGroup("msg",`
` [ValueError(), KeyError()])` | • Groups **multiple exceptions** together
• handled with `except*` syntax (Python 3.11+). | | [**except***](https://docs.python.org/3/reference/compound_stmts.html#except-star) | `except* ValueError as eg:` | • Catches matching exceptions from an **ExceptionGroup**
• multiple `except*` clauses can match different types (Python 3.11+). | | [**Bare except (avoid)**](https://docs.python.org/3/tutorial/errors.html#handling-exceptions) | `except:` | • Catches all exceptions
• **dangerous**—can hide bugs, use sparingly. | ## Table 11: File Operations | **Technique** | **Example** | **Description** | |---|---|---| | [**open() for reading**](https://docs.python.org/3/library/functions.html#open) | `f = open("file.txt", "r")` | • Opens text file
• **mode "r" is default**
• must close manually. | | [**with statement**](https://docs.python.org/3/reference/compound_stmts.html#with) | `with open("f.txt") as f:` | • Context manager
• **auto-closes** file even if exception occurs. | | [**read()**](https://docs.python.org/3/library/io.html#io.TextIOBase.read) | `content = f.read()` | • Reads entire file as string
• **memory-intensive** for large files. | | [**readline()**](https://docs.python.org/3/library/io.html#io.TextIOBase.readline) | `line = f.readline()` | • Reads single line
• **includes newline** character. | | [**readlines()**](https://docs.python.org/3/library/io.html#io.IOBase.readlines) | `lines = f.readlines()` | • Returns list of all lines
• **newlines preserved**. | | [**Iterate file**](https://docs.python.org/3/tutorial/inputoutput.html#methods-of-file-objects) | `for line in f:` | • Memory-efficient line iteration
• **preferred over readlines()** for large files. | | [**write()**](https://docs.python.org/3/library/io.html#io.TextIOBase.write) | `f.write("text")` | • Writes string to file
• **doesn't add newline** automatically. | | [**writelines()**](https://docs.python.org/3/library/io.html#io.IOBase.writelines) | `f.writelines(lines)` | • Writes sequence of strings
• **no newlines added**. | | [**Mode "w"**](https://docs.python.org/3/library/functions.html#open) | `open("f.txt", "w")` | • Write mode
• **truncates existing** file or creates new. | | [**Mode "a"**](https://docs.python.org/3/library/functions.html#open) | `open("f.txt", "a")` | • Append mode
• **adds to end** of existing file. | | [**Mode "b"**](https://docs.python.org/3/library/functions.html#open) | `open("f.bin", "rb")` | • Binary mode
• for **non-text files**
• returns bytes objects. | | [**pathlib.Path**](https://docs.python.org/3/library/pathlib.html) | `Path("f.txt").read_text()` | • Object-oriented paths
• **cleaner API** than os.path
• `copy()` and `move()` methods added in 3.14. | ## Table 12: Modules and Imports | **Technique** | **Example** | **Description** | |---|---|---| | [**import module**](https://docs.python.org/3/tutorial/modules.html#modules) | `import math` | • Imports entire module
• **access via `math.func()`**. | | [**from import**](https://docs.python.org/3/tutorial/modules.html#more-on-modules) | `from math import sqrt` | • Imports specific names
• **directly accessible** without prefix. | | [**import as**](https://docs.python.org/3/tutorial/modules.html#more-on-modules) | `import numpy as np` | • Aliases module
• **shorter name** for convenience. | | [**from import ***](https://docs.python.org/3/tutorial/modules.html#more-on-modules) | `from math import *` | • Imports all public names
• **discouraged**—pollutes namespace. | | [**Relative imports**](https://docs.python.org/3/tutorial/modules.html#intra-package-references) | `from . import sibling` | • Within packages
• **dot notation** for current/parent package. | | [**__init__.py**](https://docs.python.org/3/tutorial/modules.html#packages) | `pkg/__init__.py` | • Makes directory a package
• can **initialize package** and control imports. | | [**if __name__ == "__main__"**](https://docs.python.org/3/library/__main__.html) | `if __name__ == "__main__":` | • Checks if script is **run directly** vs imported
• guards executable code. | | [**sys.path**](https://docs.python.org/3/library/sys.html#sys.path) | `sys.path.append(dir)` | • Module search paths
• **modify to add** custom locations. | | [**importlib**](https://docs.python.org/3/library/importlib.html) | `importlib.import_module(name)` | • Dynamic imports
• **import by string name** at runtime. | ## Table 13: Common Built-in Functions | **Function** | **Example** | **Description** | |---|---|---| | [**len()**](https://docs.python.org/3/library/functions.html#len) | `len([1, 2, 3])` | • Returns length of sequence or collection
• **calls `__len__`** method. | | [**range()**](https://docs.python.org/3/library/functions.html#func-range) | `range(start, stop, step)` | • Generates arithmetic sequence
• **stop is exclusive**. | | [**enumerate()**](https://docs.python.org/3/library/functions.html#enumerate) | `enumerate(items, start=0)` | • Adds counter to iterable
• returns **(index, value)** pairs. | | [**zip()**](https://docs.python.org/3/library/functions.html#zip) | `zip(list1, list2)` | • Pairs elements from iterables
• **stops at shortest** input
• `strict=True` raises if lengths differ (3.10+). | | [**map()**](https://docs.python.org/3/library/functions.html#map) | `map(func, iterable)` | • Applies function to each element
• returns **lazy iterator**. | | [**filter()**](https://docs.python.org/3/library/functions.html#filter) | `filter(predicate, items)` | • Filters elements where predicate is **truthy**
• lazy iterator. | | [**sum()**](https://docs.python.org/3/library/functions.html#sum) | `sum(numbers, start=0)` | • Sums numeric iterable
• **optional starting value**. | | [**sorted()**](https://docs.python.org/3/library/functions.html#sorted) | `sorted(items, key=func)` | • Returns new sorted list
• **doesn't modify** original. | | [**min() / max()**](https://docs.python.org/3/library/functions.html#min) | `min(items, key=func)` | • Returns smallest/largest element
• **optional key function**. | | [**all()**](https://docs.python.org/3/library/functions.html#all) | `all([True, True, False])` | Returns `True` if **all elements** truthy or iterable empty. | | [**any()**](https://docs.python.org/3/library/functions.html#any) | `any([False, False, True])` | Returns `True` if **any element** truthy. | | [**reversed()**](https://docs.python.org/3/library/functions.html#reversed) | `reversed(seq)` | • Returns reverse iterator
• **doesn't modify** original. | | [**isinstance()**](https://docs.python.org/3/library/functions.html#isinstance) | `isinstance(obj, type)` | • Checks object type
• **accepts tuple** of types. | | [**type()**](https://docs.python.org/3/library/functions.html#type) | `type(obj)` | • Returns object's type
• **for checking use isinstance()** instead. | | [**input()**](https://docs.python.org/3/library/functions.html#input) | `input("Enter: ")` | • Reads line from stdin
• **always returns string**. | | [**print()**](https://docs.python.org/3/library/functions.html#print) | `print(*values, sep=" ")` | • Writes to stdout
• **customizable separator and ending**. | ## Table 14: Itertools Module | **Function** | **Example** | **Description** | |---|---|---| | [**count()**](https://docs.python.org/3/library/itertools.html#itertools.count) | `count(start=0, step=1)` | • Infinite counter
• **useful with `zip()` or `takewhile()`**. | | [**cycle()**](https://docs.python.org/3/library/itertools.html#itertools.cycle) | `cycle([1, 2, 3])` | • Repeats iterable infinitely
• **saves copy** of all elements. | | [**repeat()**](https://docs.python.org/3/library/itertools.html#itertools.repeat) | `repeat(10, times=3)` | • Repeats object n times
• **infinite if times omitted**. | | [**chain()**](https://docs.python.org/3/library/itertools.html#itertools.chain) | `chain(it1, it2)` | • Concatenates iterables
• **flattens** into single iterator. | | [**pairwise()**](https://docs.python.org/3/library/itertools.html#itertools.pairwise) | `pairwise([1, 2, 3])` | • Returns **overlapping pairs** of consecutive elements
• yields `(1,2), (2,3)` (Python 3.10+). | | [**batched()**](https://docs.python.org/3/library/itertools.html#itertools.batched) | `batched(range(10), 3)` | • Splits iterable into **fixed-size tuples**
• last batch may be shorter (Python 3.12+). | | [**combinations()**](https://docs.python.org/3/library/itertools.html#itertools.combinations) | `combinations(items, r)` | • All r-length combinations
• **order doesn't matter**, no repeats. | | [**permutations()**](https://docs.python.org/3/library/itertools.html#itertools.permutations) | `permutations(items, r)` | • All r-length permutations
• **order matters**. | | [**product()**](https://docs.python.org/3/library/itertools.html#itertools.product) | `product(a, b)` | • Cartesian product
• equivalent to **nested for-loops**. | | [**groupby()**](https://docs.python.org/3/library/itertools.html#itertools.groupby) | `groupby(items, key=func)` | • Groups consecutive elements by key
• **input must be sorted** by same key. | | [**islice()**](https://docs.python.org/3/library/itertools.html#itertools.islice) | `islice(it, start, stop)` | • Slices iterator
• **doesn't support negative indices**. | | [**accumulate()**](https://docs.python.org/3/library/itertools.html#itertools.accumulate) | `accumulate(nums, func)` | • Running totals or reductions
• **default is sum**. | | [**takewhile()**](https://docs.python.org/3/library/itertools.html#itertools.takewhile) | `takewhile(pred, it)` | • Yields elements **while predicate true**
• stops at first false. | | [**dropwhile()**](https://docs.python.org/3/library/itertools.html#itertools.dropwhile) | `dropwhile(pred, it)` | • Skips elements **while predicate true**
• yields rest. | | [**zip_longest()**](https://docs.python.org/3/library/itertools.html#itertools.zip_longest) | `zip_longest(a, b, fill=None)` | Like `zip()` but **continues to longest** input with fillvalue. | ## Table 15: Decorators | **Technique** | **Example** | **Description** | |---|---|---| | [**Function decorator**](https://docs.python.org/3/glossary.html#term-decorator) | `@decorator`
`def func():` | • Wraps function to **modify behavior**
• syntax sugar for `func = decorator(func)`. | | [**Simple decorator**](https://realpython.com/primer-on-python-decorators/) | `def deco(f):`
` def wrap():`
` return f()`
` return wrap` | • Returns wrapper function
• **replaces original** function. | | [**functools.wraps**](https://docs.python.org/3/library/functools.html#functools.wraps) | `@wraps(f)`
`def wrapper():` | • Preserves function **metadata** (`__name__`, `__doc__`)
• use in decorator wrappers. | | [**Decorator with args**](https://realpython.com/primer-on-python-decorators/) | `@deco(arg)`
`def func():` | • Returns decorator
• **three-level nesting**: `deco(arg)(func)()`. | | [**Class decorator**](https://docs.python.org/3/reference/compound_stmts.html#class-definitions) | `@deco`
`class MyClass:` | • Modifies or replaces class
• **callable returns class**. | | [**Method decorator**](https://docs.python.org/3/library/functions.html#staticmethod) | `@staticmethod`
`def method():` | **Built-in decorators** like `@classmethod`, `@staticmethod`, `@property`. | | [**Stacking decorators**](https://realpython.com/primer-on-python-decorators/) | `@deco1`
`@deco2`
`def f():` | • Multiple decorators
• applied **bottom-up**: `deco1(deco2(f))`. | | [**lru_cache**](https://docs.python.org/3/library/functools.html#functools.lru_cache) | `@lru_cache(maxsize=128)` | • Memoizes function results
• **significant speedup** for repeated calls. | | [**functools.cache**](https://docs.python.org/3/library/functools.html#functools.cache) | `@cache` | • Simpler unbounded memoization
• shorthand for **`lru_cache(maxsize=None)`** (Python 3.9+). | ## Table 16: Context Managers | **Technique** | **Example** | **Description** | |---|---|---| | [**with statement**](https://docs.python.org/3/reference/compound_stmts.html#with) | `with open("f") as f:` | • Ensures resource cleanup
• **calls `__enter__` and `__exit__`**. | | [**Multiple contexts**](https://docs.python.org/3/reference/compound_stmts.html#with) | `with open("a") as f1, open("b") as f2:` | • Manages multiple resources
• **left-to-right acquisition**. | | [**contextlib.contextmanager**](https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager) | `@contextmanager`
`def ctx():` | • Creates context manager from generator
• **`yield` separates setup/teardown**. | | [**Custom __enter__ / __exit__**](https://docs.python.org/3/reference/datamodel.html#context-managers) | `def __enter__(self):`
` return self` | • Implement protocol manually
• **`__exit__` gets exception info**. | | [**contextlib.suppress**](https://docs.python.org/3/library/contextlib.html#contextlib.suppress) | `with suppress(FileNotFoundError):` | • Ignores specified exceptions
• **cleaner than try-except pass**. | | [**contextlib.closing**](https://docs.python.org/3/library/contextlib.html#contextlib.closing) | `with closing(obj):` | • Calls `close()` on exit
• for **objects without context manager**. | | [**ExitStack**](https://docs.python.org/3/library/contextlib.html#contextlib.ExitStack) | `with ExitStack() as stack:` | Manages **variable number** of context managers dynamically. | ## Table 17: Async/Await (Asyncio) | **Technique** | **Example** | **Description** | |---|---|---| | [**async def**](https://docs.python.org/3/library/asyncio-task.html#coroutines) | `async def fetch():` | • Defines coroutine function
• **must be awaited** or scheduled as task. | | [**await**](https://docs.python.org/3/reference/expressions.html#await) | `result = await coro()` | • Suspends coroutine
• **yields control** to event loop until result ready. | | [**asyncio.run()**](https://docs.python.org/3/library/asyncio-task.html#asyncio.run) | `asyncio.run(main())` | • Entry point
• **creates event loop** and runs coroutine. | | [**asyncio.create_task()**](https://docs.python.org/3/library/asyncio-task.html#asyncio.create_task) | `task = create_task(coro())` | • Schedules coroutine
• **runs concurrently** with other tasks. | | [**asyncio.gather()**](https://docs.python.org/3/library/asyncio-task.html#asyncio.gather) | `await gather(coro1(), coro2())` | • Runs multiple coroutines concurrently
• **waits for all** to complete. | | [**asyncio.TaskGroup**](https://docs.python.org/3/library/asyncio-task.html#asyncio.TaskGroup) | `async with TaskGroup() as tg:`
` tg.create_task(coro())` | • Structured concurrency
• **auto-cancels** remaining tasks on failure (Python 3.11+). | | [**asyncio.timeout()**](https://docs.python.org/3/library/asyncio-task.html#asyncio.timeout) | `async with asyncio.timeout(5):` | • Context manager with **deadline**
• raises `TimeoutError` if exceeded (Python 3.11+). | | [**asyncio.wait_for()**](https://docs.python.org/3/library/asyncio-task.html#asyncio.wait_for) | `await wait_for(coro(), timeout=5)` | • Adds timeout to coroutine
• **raises TimeoutError** if exceeded. | | [**async for**](https://docs.python.org/3/reference/compound_stmts.html#async-for) | `async for item in async_iter:` | • Iterates over **async iterable**
• calls `__aiter__` and `__anext__`. | | [**async with**](https://docs.python.org/3/reference/compound_stmts.html#async-with) | `async with resource:` | • Async context manager
• **awaits `__aenter__` and `__aexit__`**. | | [**asyncio.sleep()**](https://docs.python.org/3/library/asyncio-task.html#asyncio.sleep) | `await asyncio.sleep(1)` | • Non-blocking sleep
• **yields control** to other coroutines. | ## Table 18: Type Hints | **Technique** | **Example** | **Description** | |---|---|---| | [**Basic types**](https://docs.python.org/3/library/typing.html) | `x: int = 5` | • Annotates variable type
• **not enforced** at runtime. | | [**Function annotations**](https://docs.python.org/3/library/typing.html) | `def f(x: int) -> str:` | • Parameter and return types
• used by **type checkers** like mypy. | | [**List[T]**](https://docs.python.org/3/library/typing.html#typing.List) | `items: List[int]` | • Homogeneous list
• **generic type** with element type. | | [**Dict[K, V]**](https://docs.python.org/3/library/typing.html#typing.Dict) | `d: Dict[str, int]` | **Dictionary with specific key/value types.** | | [**Optional[T]**](https://docs.python.org/3/library/typing.html#typing.Optional) | `x: Optional[int] = None` | • Shorthand for `Union[T, None]`
• **accepts value or None**. | | [**Union[T1, T2]**](https://docs.python.org/3/library/typing.html#typing.Union) | `x: Union[int, str]` | • Multiple allowed types
• **modern syntax** int | str (Python 3.10+). | | [**Tuple[T, ...]**](https://docs.python.org/3/library/typing.html#typing.Tuple) | `t: Tuple[int, str]` | • Fixed-length tuple with specific types
• `...` for **variable length**. | | [**Callable**](https://docs.python.org/3/library/typing.html#typing.Callable) | `f: Callable[[int], str]` | • Function type
• **list of param types, return type**. | | [**Any**](https://docs.python.org/3/library/typing.html#typing.Any) | `x: Any` | • Disables type checking
• **avoid when possible**. | | [**TypeVar**](https://docs.python.org/3/library/typing.html#typing.TypeVar) | `T = TypeVar('T')` | • Generic type variable
• for **parametric polymorphism**. | | [**Protocol**](https://docs.python.org/3/library/typing.html#typing.Protocol) | `class Sized(Protocol):` | • Structural subtyping
• **duck typing** with type hints. | | [**Literal**](https://docs.python.org/3/library/typing.html#typing.Literal) | `x: Literal["a", "b"]` | • Restricts to **specific values**
• for constants. | | [**type statement**](https://docs.python.org/3/reference/simple_stmts.html#the-type-statement) | `type Vector = list[float]` | • Declares **type alias** with lazy evaluation
• replaces `TypeAlias` annotation (Python 3.12+). | | [**Type parameter syntax**](https://peps.python.org/pep-0695/) | `def f[T](x: T) -> T:` | • Inline **generic type variables** on functions and classes
• replaces `TypeVar` boilerplate (Python 3.12+). | | [**TypeIs**](https://docs.python.org/3/library/typing.html#typing.TypeIs) | `def is_str(x) -> TypeIs[str]:` | • **Narrows type** in both if/else branches
• safer than `TypeGuard` (Python 3.13+). | | [**@override**](https://docs.python.org/3/library/typing.html#typing.override) | `@override`
`def method(self):` | • Marks method as **overriding parent**
• type checkers flag mismatches (Python 3.12+). | ## Table 19: Regular Expressions | **Function** | **Example** | **Description** | |---|---|---| | [**re.match()**](https://docs.python.org/3/library/re.html#re.match) | `re.match(r"\d+", s)` | • Matches **at start** of string only
• returns match object or None. | | [**re.search()**](https://docs.python.org/3/library/re.html#re.search) | `re.search(r"\d+", s)` | • Searches **anywhere** in string
• returns first match. | | [**re.findall()**](https://docs.python.org/3/library/re.html#re.findall) | `re.findall(r"\d+", s)` | • Returns **list of all matches**
• non-overlapping. | | [**re.finditer()**](https://docs.python.org/3/library/re.html#re.finditer) | `re.finditer(r"\d+", s)` | • Returns **iterator of match objects**
• memory-efficient for large inputs. | | [**re.sub()**](https://docs.python.org/3/library/re.html#re.sub) | `re.sub(r"\d+", "X", s)` | • Replaces matches
• **accepts function** as replacement. | | [**re.split()**](https://docs.python.org/3/library/re.html#re.split) | `re.split(r"\s+", s)` | • Splits by pattern
• **preserves groups** in result. | | [**re.compile()**](https://docs.python.org/3/library/re.html#re.compile) | `p = re.compile(r"\d+")` | • Precompiles pattern
• **faster for reuse**. | | [**Groups**](https://docs.python.org/3/library/re.html#regular-expression-objects) | `m.group(1)` | • Captures subpatterns
• **`group(0)` is entire match**. | | [**Named groups**](https://docs.python.org/3/library/re.html#regular-expression-objects) | `(?P\d+)` | • Named capture
• access via **`m.group('name')`**. | | [**re.IGNORECASE**](https://docs.python.org/3/library/re.html#re.IGNORECASE) | `re.search(r"a", s, re.I)` | • Case-insensitive matching
• **multiple flags** with re.I | re.M. | | [**Raw strings**](https://docs.python.org/3/reference/lexical_analysis.html#string-and-bytes-literals) | `r"\d+"` | • Prefix with `r`
• **avoids double-escaping** backslashes. | ## Table 20: Dataclasses and Modern Class Features | **Technique** | **Example** | **Description** | |---|---|---| | [**@dataclass**](https://docs.python.org/3/library/dataclasses.html) | `@dataclass`
`class Point:` | • Auto-generates `__init__`, `__repr__`, etc.
• **less boilerplate** (Python 3.7+). | | [**Field with default**](https://docs.python.org/3/library/dataclasses.html#dataclasses.field) | `x: int = 0` | • Default values
• **mutable defaults** require `field(default_factory=...)`. | | [**field()**](https://docs.python.org/3/library/dataclasses.html#dataclasses.field) | `items: list = field(default_factory=list)` | • Customizes field behavior
• **prevents shared mutable defaults**. | | [**frozen=True**](https://docs.python.org/3/library/dataclasses.html) | `@dataclass(frozen=True)` | • Makes instances immutable
• **enables hashing** for use as dict keys. | | [**slots=True**](https://docs.python.org/3/library/dataclasses.html) | `@dataclass(slots=True)` | • Generates `__slots__` for **reduced memory**
• prevents dynamic attribute creation (Python 3.10+). | | [**kw_only=True**](https://docs.python.org/3/library/dataclasses.html) | `@dataclass(kw_only=True)` | • Forces **keyword-only** arguments in `__init__`
• prevents positional mistakes (Python 3.10+). | | [**__post_init__**](https://docs.python.org/3/library/dataclasses.html#post-init-processing) | `def __post_init__(self):` | • Runs after `__init__`
• for **computed fields** or validation. | | [**InitVar**](https://docs.python.org/3/library/dataclasses.html#init-only-variables) | `temp: InitVar[int]` | • Init-only variable
• **not stored as field**, available in `__post_init__`. | | [**asdict() / astuple()**](https://docs.python.org/3/library/dataclasses.html#dataclasses.asdict) | `asdict(obj)` | • Converts dataclass to dict/tuple
• **shallow copy** by default. | | [**attrs**](https://www.attrs.org/) | `@define`
`class C:` | • Third-party alternative
• **more features** than dataclasses. | | [**Pydantic**](https://docs.pydantic.dev/) | `class User(BaseModel):` | • Data validation library
• **runtime type checking** and JSON schema. | ## Table 21: Virtual Environments and Package Management | **Command** | **Example** | **Description** | |---|---|---| | [**venv creation**](https://docs.python.org/3/library/venv.html) | `python -m venv myenv` | • Creates isolated environment
• **includes own Python and pip**. | | [**Activation (Unix)**](https://docs.python.org/3/library/venv.html) | `source myenv/bin/activate` | • Activates environment
• **modifies PATH** to use venv Python. | | [**Activation (Windows)**](https://docs.python.org/3/library/venv.html) | `myenv\Scripts\activate.bat` | • Windows activation
• **PowerShell uses activate.ps1**. | | [**Deactivation**](https://docs.python.org/3/library/venv.html) | `deactivate` | • Returns to system Python
• **works on all platforms**. | | [**pip install**](https://pip.pypa.io/en/stable/cli/pip_install/) | `pip install package` | • Installs package
• **use -U for upgrade**. | | [**uv**](https://docs.astral.sh/uv/) | `uv pip install package` | • **Ultra-fast** Rust-based package manager
• drop-in replacement for pip, venv, and pip-tools. | | [**pip freeze**](https://pip.pypa.io/en/stable/cli/pip_freeze/) | `pip freeze > requirements.txt` | • Exports installed packages
• **pinned versions** for reproducibility. | | [**pip install -r**](https://pip.pypa.io/en/stable/cli/pip_install/) | `pip install -r requirements.txt` | • Installs from requirements file
• **exact versions** specified. | | [**pip list**](https://pip.pypa.io/en/stable/cli/pip_list/) | `pip list` | • Shows installed packages
• **`--outdated` flag** checks for updates. | | [**pip show**](https://pip.pypa.io/en/stable/cli/pip_show/) | `pip show package` | • Package details
• **shows dependencies** and install location. | | [**pip uninstall**](https://pip.pypa.io/en/stable/cli/pip_uninstall/) | `pip uninstall package` | • Removes package
• **prompts for confirmation**. | ## Table 22: Advanced Patterns and Idioms | **Pattern** | **Example** | **Description** | |---|---|---| | [**EAFP**](https://docs.python.org/3/glossary.html#term-EAFP) | `try:`
` d[k]`
`except KeyError:` | • Easier to Ask Forgiveness than Permission
• **Pythonic error handling**. | | [**LBYL**](https://docs.python.org/3/glossary.html#term-LBYL) | `if k in d:`
` x = d[k]` | • Look Before You Leap
• **less Pythonic**, can have race conditions. | | [**Chained comparison**](https://docs.python.org/3/reference/expressions.html#comparisons) | `1 < x < 10` | • Multiple comparisons
• **more readable** than `1 < x and x < 10`. | | [**Unpacking**](https://docs.python.org/3/tutorial/controlflow.html#unpacking-argument-lists) | `a, b, *rest = items` | • Extended unpacking
• **`*rest` captures remaining** (Python 3.0+). | | [**Dict get() with default**](https://docs.python.org/3/library/stdtypes.html#dict.get) | `d.get(key, default)` | • Safe access
• **returns default** if key missing, doesn't raise. | | [**setdefault()**](https://docs.python.org/3/library/stdtypes.html#dict.setdefault) | `d.setdefault(k, []).append(x)` | • Gets or creates
• **single lookup** vs get + assignment. | | [**defaultdict**](https://docs.python.org/3/library/collections.html#collections.defaultdict) | `from collections import defaultdict` | • Auto-creates missing keys
• **cleaner than setdefault** for repeated use. | | [**Counter**](https://docs.python.org/3/library/collections.html#collections.Counter) | `Counter(items)` | • Counts hashable objects
• **dict subclass** with counting methods. | | [**namedtuple**](https://docs.python.org/3/library/collections.html#collections.namedtuple) | `Point = namedtuple('Point', 'x y')` | • Tuple with named fields
• **immutable, memory-efficient** alternative to class. | | [**StrEnum**](https://docs.python.org/3/library/enum.html#enum.StrEnum) | `class Color(StrEnum):`
` RED = auto()` | • Enum with **string values**
• members usable directly as strings (Python 3.11+). | | [**ChainMap**](https://docs.python.org/3/library/collections.html#collections.ChainMap) | `ChainMap(dict1, dict2)` | • Groups multiple dicts
• **searches sequentially** without copying. | | [**functools.reduce()**](https://docs.python.org/3/library/functools.html#functools.reduce) | `reduce(lambda x,y: x+y, nums)` | • Cumulative operation
• **apply function** cumulatively to sequence. | | [**functools.partial()**](https://docs.python.org/3/library/functools.html#functools.partial) | `partial(func, arg1)` | • Partially applies arguments
• **creates new callable** with fixed params. | | [**functools.singledispatch()**](https://docs.python.org/3/library/functools.html#functools.singledispatch) | `@singledispatch`
`def process(arg):` | • **Type-based function overloading**
• dispatches on first argument type. | | [**Singleton pattern**](https://python-patterns.guide/gang-of-four/singleton/) | `class Singleton(type):` | • Ensures single instance
• **use metaclass or module** for implementation. |

Python Cheat Sheet

Python Cheat Sheet

Python Cheat Sheet

Python Cheat Sheet