Python

Python Cheat Sheet 1. Basic Syntax Comments # Single-line comment """ Multi-line comment """ def function(): """ Docstring: used for function/class/module documentation """ pass Variables and Data Types # Python uses dynamic typing name = "Bob" # str age = 30 # int height = 1.75 # float is_student = True # bool numbers = [1, 2, 3] # list person = {"name": "Alice", "age": 25} # dict unique_numbers = {1, 2, 3} # set coordinates = (x, y) # tuple Constants # Python doesn't have built-in constant types # Convention: use uppercase for constants PI = 3.14159 MAX_SIZE = 100 Operators # Arithmetic: +, -, *, /, // (integer division), %, ** # Comparison: ==, !=, <, >, <=, >= # Logical: and, or, not # Identity: is, is not # Membership: in, not in Type Conversion x = 10 y = float(x) # Convert to float s = str(x) # Convert to string 2. Control Structures Conditional Statements if condition: # code elif other_condition: # code else: # code # Ternary operator x = value_if_true if condition else value_if_false # Match statement (Python 3.10+) match value: case pattern1: # code case pattern2: # code case _: # default case Loops for item in iterable: # code for i in range(5): # code while condition: # code # List comprehension squares = [x**2 for x in range(10)] # Dictionary comprehension square_dict = {x: x**2 for x in range(5)} 3. Functions Function Declaration and Definition def greet(name): return f"Hello, {name}!" # Lambda function multiply = lambda x, y: x * y Parameters and Return Values # Default parameters def greet(name, greeting="Hello"): return f"{greeting}, {name}!" # Arbitrary arguments def sum_all(*args): return sum(args) # Keyword arguments def person_info(**kwargs): for key, value in kwargs.items(): print(f"{key}: {value}") # Type hinting (Python 3.5+) def add(a: int, b: int) -> int: return a + b 4. Data Structures Lists fruits = ['apple', 'banana', 'cherry'] fruits.append('date') first_fruit = fruits[0] sliced_fruits = fruits[1:3] # ['banana', 'cherry'] Dictionaries person = {'name': 'Alice', 'age': 30} person['city'] = 'New York' age = person.get('age') Sets unique_numbers = {1, 2, 3, 4, 5} unique_numbers.add(6) Tuples point = (10, 20) x, y = point # Unpacking 5. Object-Oriented Programming Classes and Objects class Person: def __init__(self, name, age): self.name = name self.age = age def greet(self): return f"Hello, I'm {self.name}" person = Person("Alice", 30) print(person.greet()) Inheritance class Student(Person): def __init__(self, name, age, school): super().__init__(name, age) self.school = school Encapsulation class BankAccount: def __init__(self, balance): self._balance = balance # Protected attribute @property def balance(self): return self._balance 6. Exception Handling try: # code that might raise an exception except SpecificError as e: # handle specific exception except Exception as e: # handle any exception else: # executed if no exception occurs finally: # always executed 7. File I/O # Reading with open('file.txt', 'r') as file: content = file.read() # Writing with open('file.txt', 'w') as file: file.write('Hello, Python!') 8. Modules and Packages # Importing import math from datetime import datetime import numpy as np # Creating a module # In mymodule.py def my_function(): pass # Using the module import mymodule mymodule.my_function() 9. Standard Library os: Operating system interface sys: System-specific parameters and functions datetime: Date and time handling math: Mathematical functions random: Generate random numbers json: JSON encoder and decoder re: Regular expressions 10. Concurrency # Threading import threading def worker(): print("Worker thread") thread = threading.Thread(target=worker) thread.start() # Asyncio (Python 3.5+) import asyncio async def main(): print('Hello') await asyncio.sleep(1) print('World') asyncio.run(main()) 11. Context Managers class MyContext: def __enter__(self): print("Entering context") return self def __exit__(self, exc_type, exc_value, traceback): print("Exiting context") with MyContext() as ctx: print("Inside context") 12. Important Language-Specific Features List/Dict/Set comprehensions Generators and iterators Decorators Type hinting (Python 3.5+) f-strings (Python 3.6+) Walrus operator := (Python 3.8+) 13. Best Practices and Style Guide Follow PEP 8 style guide Use meaningful variable and function names Write docstrings for functions, classes, and modules Use virtual environments for project isolation Prefer import over from ... import * 14. Useful Resources Official Documentation: https://docs.python.org/ Python Package Index (PyPI): https://pypi.org/ Real Python Tutorials: https://realpython.com/ PEP 8 Style Guide: https://pep8.org/