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Python (Standard Libraries) Cheat Sheet (DRAFT) by

Cheatsheet on command standard libraries on Python

This is a draft cheat sheet. It is a work in progress and is not finished yet.

@dataclass

from dataclasses import dataclass

@dataclass
class my_class:
    field_one: type_one
    field_two: type_two
    field_three: type_three

# automatically gets __init__, __repr__, and __eq__
my_instance = my_class(
    field_one=value_one,
    field_two=value_two,
    field_three=value_three
)
A decorator that automa­tically generates __init__, __repr__, and __eq__ methods from class fields.
Each field is declared with its name and type annotation — no need to write a constr­uctor manually.
Part of the standard library via from datacl­asses import dataclass.
  

io

import io

# in-memory binary stream
binary_buffer = io.BytesIO(b"some bytes")
binary_buffer.read()         # read all bytes
binary_buffer.read(4)        # read exactly 4 bytes from cursor position
binary_buffer.write(b"more") # write bytes
binary_buffer.seek(0)        # move cursor back to start

# in-memory text stream
text_buffer = io.StringIO("some text")
text_buffer.read()           # read all text
text_buffer.read(4)          # read exactly 4 characters
text_buffer.seek(0)          # move cursor back to start
Python's standard library module for working with streams and file-like objects.
Provides in-memory file objects that behave exactly like real files but exist only in RAM.
BytesIO is for binary data, StringIO is for text data.
read(n) reads exactly n bytes from the current cursor position — useful for parsing binary formats where you need to read fixed-size chunks.
  

struct

import struct

# endianness prefix
# < = little-endian (least significant byte first, most common)
# > = big-endian    (most significant byte first, used in network protocols)

# type codes
# b = int8     B = uint8
# h = int16    H = uint16
# i = int32    I = uint32
# q = int64    Q = uint64
# f = float32  d = float64
# s = char[]   ? = bool

# repeating type codes — t = any type code
# t = one value    tt = two values    ttt = three values

# unpack — read bytes into Python values
value: int = struct.unpack("<i", f.read(4))[0]           # read one int32
a: int; b: int = struct.unpack("<ii", f.read(8))         # read two int32s
three_ints: tuple = struct.unpack("<iii", f.read(12))    # read three int32s

# pack — convert Python values into bytes
data: bytes = struct.pack("<i", 42)                      # write one int32
data: bytes = struct.pack("<ii", 42, 100)                # write two int32s
Converts between Python values and C-style binary data using format strings.
struct.un­pac­k(f­ormat, bytes) reads bytes and returns a tuple of Python values.
struct.pa­ck(­format, values) converts Python values into bytes.