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Python Basics Quick Reference

A concise overview of common Python syntax and patterns. Use this as a refresher when writing simple scripts or reviewing key language features.

Variables and Types

  • Assign variables with =
  • Basic types: int, float, str, bool
  • Multiple assignment: x, y = 1, 2
  • Type conversion: int("3"), float("3.14")
my_int: int = 5
my_float: float = 3.14
my_str: str = "hello"
my_bool: bool = True

Collections

  • List: ordered, mutable
  • Tuple: ordered, immutable
  • Dictionary: key–value store
  • Set: unordered unique items
colors: list[str] = ["red", "green", "blue"]
point: tuple[int, int] = (3, 4)
config: dict[str, str] = {"host": "localhost", "port": "8080"}
tags: set[str] = {"python", "basics"}

Control Flow

# Conditional
if condition:
    ...
elif other_condition:
    ...
else:
    ...

# Looping
for item in iterable:
    ...

while expression:
    ...

graph TD;
    A[Start] --> B{Condition?};
    B -- Yes --> C[Execute body];
    C --> B;
    B -- No --> D[Continue];

Functions

  • Define with def
  • Document using triple-quoted docstrings
  • Default and keyword arguments
  • Return values with return
def greet(name: str, excited: bool = False) -> str:
    """Return a friendly greeting for ``name``.

    Args:
        name (str): Person to greet.
        excited (bool, optional): Add an exclamation if ``True``.

    Returns:
        str: Personalized greeting.
    """
    base = f"Hello, {name}"
    return base + "!" if excited else base

Modules and Imports

import math
from pathlib import Path

Use if __name__ == "__main__": to run code when a file executes directly.

Exceptions

try:
    risky_operation()
except ValueError as err:
    print(f"Problem: {err}")

Basic I/O

user_input = input("Enter value: ")
print("You typed", user_input)

Further Reading