Python Cheatsheet - Command Reference
All the Python syntax you need for daily development — from basics to advanced features, organized by category, ready to copy into your code.
Back to LanguagesVirtual Environment & Package Management 8
python3 -m venv venvCreate a virtual environment
source venv/bin/activateActivate virtual environment (Linux/Mac)
venv\Scripts\activateActivate virtual environment (Windows)
deactivateDeactivate virtual environment
pip install packageInstall a package
pip install -r requirements.txtInstall dependencies from file
pip freeze > requirements.txtExport current environment dependencies
pip listList installed packages
Data Types 7
list = [1, 2, 3]List, mutable ordered sequence
tuple = (1, 2, 3)Tuple, immutable ordered sequence
dict = {"key": "value"}Dictionary, key-value pairs
set = {1, 2, 3}Set, unordered unique elements
str = "hello"String, immutable sequence
type(obj)Check object type
isinstance(obj, int)Check if object is an instance of a type
List Comprehension 5
[x*2 for x in range(10)]Basic list comprehension
[x for x in range(10) if x % 2 == 0]List comprehension with condition
{x: x*2 for x in range(5)}Dictionary comprehension
{x for x in range(10) if x % 2 == 0}Set comprehension
list(map(lambda x: x*2, [1,2,3]))Functional equivalent of comprehension
File I/O 8
with open("file.txt", "r") as f:Read file (recommended with auto-close)
content = f.read()Read all content
lines = f.readlines()Read all lines into a list
with open("file.txt", "w") as f:Write file (overwrite)
f.write("content")Write string
with open("file.txt", "a") as f:Append mode
import json; json.load(f)Read JSON file
json.dump(data, f, indent=2)Write JSON file
Exception 8
try:Attempt to execute code
result = 10 / 0Code that may raise an exception
except ZeroDivisionError as e:Catch a specific exception
print(f"Error: {e}")Handle exception
except Exception as e:Catch all exceptions (fallback)
else:Execute when no exception
finally:Always execute regardless of exception
raise ValueError("msg")Raise an exception explicitly
Built-in 8
len(obj)Return object length
range(start, stop, step)Generate integer sequence
enumerate(iterable)Return index-value tuples
zip(list1, list2)Zip multiple lists into tuples
sorted(iterable, key=None, reverse=False)Sort
filter(func, iterable)Filter elements
map(func, iterable)Apply function to each element
any(iterable) / all(iterable)Check if any/all are truthy
💡 Tips
- Always use the with statement for file operations to ensure proper closing, even on exceptions.
- List comprehensions are more concise and efficient than for loops, but use regular loops for complex logic.
- In Python 3, range() returns an iterator, not a list — saving memory.