Python Cheat Sheet
Learn Python from the basics →
Variables
x = "value"- Declare a variable (type inferred)
f"Hello, {name}"- f-string interpolation
type(x)- Get a variable's type
Lists & Dicts
[1, 2, 3]- List literal
{"k": "v"}- Dict literal
len(x)- Length of a list/dict/string
[x * 2 for x in arr]- List comprehension
sorted(arr)- Return a sorted copy
Strings
len(s)- String length
s.lower() / s.upper()- Change case
"x" in s- Check for a substring
s.strip()- Remove surrounding whitespace
s.split(",")- Split into a list
Control Flow
if / elif / else- Conditional branching
for x in arr:- Loop over values
for k, v in d.items():- Loop over dict entries
Functions
def f(x: str) -> str: ...- Typed function
lambda x: x * 2- Anonymous function
f(name="Ada")- Keyword argument
Classes
class User:\n def __init__(self, name): self.name = name- Class with constructor
User("Ada")- Instantiate
class Admin(User): pass- Inheritance
Exceptions
try: ...\nexcept ValueError as e: ...- Catch a specific exception
finally: ...- Always runs, error or not
raise ValueError("msg")- Raise an exception
File Handling
with open("f.txt") as file: ...- Open a file, auto-closed
file.read()- Read entire file contents
file.write("text")- Write to a file ("w" mode)
JSON & APIs
json.dumps(data)- Python dict/list -> JSON string
json.loads(text)- JSON string -> Python dict/list
requests.get(url).json()- Fetch and parse a JSON API response
Packages & Environments
python3 -m venv venv- Create a virtual environment
pip install requests- Install a package
pip freeze > requirements.txt- Record installed package versions