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Python Command Cheatsheet

Python Command Cheatsheet

Essential Python syntax and commands

Programming

Python Command Cheatsheet

A comprehensive reference for Python programming.

Basics

Data Types

# Numbers
x = 5                    # int
y = 3.14                 # float
z = 1 + 2j               # complex

# Strings
s = "Hello"
s = 'World'
s = """Multi
line"""

# Boolean
b = True
b = False

# None
n = None

Variables

x = 10
x, y = 5, 10             # Multiple assignment
x, y = y, x              # Swap

Operators

# Arithmetic
+ - * / // % **

# Comparison
== != < > <= >=

# Logical
and or not

# Identity
is is not

# Membership
in not in

Data Structures

Lists

lst = [1, 2, 3]
lst.append(4)            # Add to end
lst.insert(0, 0)         # Insert at index
lst.remove(2)            # Remove value
lst.pop()                # Remove last
lst.pop(0)               # Remove at index
lst.sort()               # Sort in place
sorted(lst)              # Return sorted
lst.reverse()            # Reverse
len(lst)                 # Length
lst[0]                   # Access
lst[-1]                  # Last element
lst[1:3]                 # Slice
lst[::-1]                # Reverse

Tuples

t = (1, 2, 3)
t = 1, 2, 3              # Without parentheses
t[0]                     # Access
# Tuples are immutable

Dictionaries

d = {'key': 'value'}
d['key']                 # Access
d.get('key', default)    # Safe access
d['new'] = 'value'       # Add/update
del d['key']             # Delete
d.keys()                 # All keys
d.values()               # All values
d.items()                # Key-value pairs
'key' in d               # Check existence

Sets

s = {1, 2, 3}
s.add(4)                 # Add element
s.remove(2)              # Remove (error if not exists)
s.discard(2)             # Remove (no error)
s1 | s2                  # Union
s1 & s2                  # Intersection
s1 - s2                  # Difference

Control Flow

If Statements

if condition:
    pass
elif condition:
    pass
else:
    pass

# Ternary
x = a if condition else b

Loops

# For loop
for item in iterable:
    print(item)

for i in range(10):
    print(i)

for i, item in enumerate(lst):
    print(i, item)

# While loop
while condition:
    pass

# Break and continue
break
continue

List Comprehension

[x*2 for x in range(10)]
[x for x in range(10) if x % 2 == 0]
{x: x*2 for x in range(5)}  # Dict comprehension
{x*2 for x in range(10)}    # Set comprehension

Functions

Function Definition

def function_name(param1, param2):
    return param1 + param2

# Default arguments
def func(a, b=10):
    return a + b

# Variable arguments
def func(*args, **kwargs):
    pass

# Lambda
lambda x: x * 2

Decorators

@decorator
def function():
    pass

# Common decorators
@staticmethod
@classmethod
@property

Classes

Class Definition

class MyClass:
    def __init__(self, value):
        self.value = value
    
    def method(self):
        return self.value

obj = MyClass(10)
obj.method()

Inheritance

class Child(Parent):
    def __init__(self):
        super().__init__()

File Operations

Read/Write Files

# Read
with open('file.txt', 'r') as f:
    content = f.read()
    lines = f.readlines()
    for line in f:
        print(line)

# Write
with open('file.txt', 'w') as f:
    f.write('text')
    f.writelines(['line1\n', 'line2\n'])

# Append
with open('file.txt', 'a') as f:
    f.write('more text')

Modules

Import

import module
from module import function
from module import *
import module as alias

Common Modules

import os
import sys
import json
import datetime
import re
import random
import math

String Methods

Common Operations

s.lower()
s.upper()
s.strip()
s.split(',')
s.replace('old', 'new')
s.startswith('prefix')
s.endswith('suffix')
s.find('substring')
s.count('char')
','.join(list)
f"Hello {name}"          # f-string

List Methods

Common Operations

lst.append(x)
lst.extend([1,2,3])
lst.insert(i, x)
lst.remove(x)
lst.pop(i)
lst.clear()
lst.index(x)
lst.count(x)
lst.sort()
lst.reverse()
lst.copy()

Exception Handling

Try-Except

try:
    # code
except Exception as e:
    print(e)
except (TypeError, ValueError):
    pass
else:
    # if no exception
finally:
    # always execute

# Raise exception
raise ValueError("message")

Virtual Environment

venv

python -m venv venv
source venv/bin/activate     # Linux/Mac
venv\Scripts\activate        # Windows
deactivate

pip

pip install package
pip install -r requirements.txt
pip freeze > requirements.txt
pip list
pip uninstall package

Quick Reference

Operation Syntax
Print print(x)
Input input("prompt")
Type type(x)
Length len(x)
Range range(10)
Enumerate enumerate(lst)
Zip zip(lst1, lst2)
Map map(func, lst)
Filter filter(func, lst)
Sum sum(lst)
Min/Max min(lst), max(lst)
Sorted sorted(lst)

Best Practices

  1. Follow PEP 8 style guide
  2. Use virtual environments
  3. Write docstrings
  4. Use list comprehensions when appropriate
  5. Handle exceptions properly
  6. Use context managers (with statement)
  7. Avoid global variables
  8. Use meaningful names
  9. Keep functions small
  10. Test your code

Resources

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