Your Ultimate Python 3 Cheat Sheet for Quick Reference

Are you new to Python programming or just need a handy reference guide? Look no further! In this blog post, we’ve compiled a comprehensive Python 3 cheat sheet that covers the essential concepts, syntax, and techniques to help you navigate the world of Python programming. Whether you’re a beginner or an experienced developer, this cheat sheet will serve as a quick and informative reference.

Python Basics

Comments

Let’s start with comments, single line comment as shown below:

# This is a single-line comment

Multiline comment as shown below :

'''
This is a
multi-line
comment
'''

Print

Variables

variable_name = value

Example :

age = 25
name = "Tom"

Here age and name are variables. Python variables are dynamically typed, so they can hold any type of data.

Data Types

Python 3 has following data types:

• int: integers
• float: floating-point numbers
• str: strings
• bool: boolean values (True/False)

• list: ordered collection of elements
• tuple: ordered, immutable collection of elements
• dict: key-value pairs
• set: unordered collection of unique elements

Control Flow

Conditional Statements

if condition:
    # code
elif another_condition:
    # code
else:
    # code

Loops

Python 3 supports the following loops.

For loop

for item in iterable:
    # code

While Loop

while condition:
    if some_condition:
        break
    elif another_condition:
        continue

Learn more about Python loop syntax

Functions

Defining Functions

def function_name(parameters):
    # code
    return result

Lambda Functions

Lambda functions are anonymous functions created using the lambda keyword.

lambda arguments: expression

Example :

lambda x, y: x + y

Scope

• Variables defined within a function are local to that function.
• Variables defined outside functions are global.

Data Structures

Lists

fruits = ["apple","oranage","banana"]

Tuples

days= ("Sunday", "Monday", "Tuesday","Wednesday","Thursday","Friday","Saturday")

Dictionaries

my_dict = {
    'key1': 'value1',
    'key2': 'value2'
}

Example :

person = {
'name': 'Tom',
'age': 30
}

Sets

my_set = {item1, item2, item3}

Example :

my_set = {1, 2, 3} 

File Handling

Opening Files

file = open('filename.txt', 'mode')

Modes :

• 'r': Read
• 'w': Write (creates a new file or truncates an existing one)
• 'a': Append
• 'b': Binary mode
• 'x': Exclusive creation (fails if file already exists)

Reading from a File

content = file.read()

Writing to a File

file.write("Hello, File!")

Exception Handling

Try-Except Blocks

try:
    # code
except SomeException:
    # code
else:
    # code (runs if no exception)
finally:
    # code (always runs)

Raising Exceptions

raise SomeException("An error occurred")

Modules

Importing Modules

import module_name
from module_name import some_function

Creating Modules

• Create a .py file and define functions and variables.
• Use import to use the module in other scripts.

Object-Oriented Programming

Classes and Objects

class MyClass:
    def __init__(self, param):
        self.attribute = param
    def some_method(self):
        # code

Inheritance

class ChildClass(ParentClass):
    # code

Useful Built-in Functions

• len(iterable): Returns the number of items in an iterable.
• range(start, stop, step): Generates a sequence of numbers.
• type(object): Returns the type of an object.
• str(object): Converts an object to a string.

Virtual Environment

Creating a Virtual Environment

python3 -m venv env_name

Activating a Virtual Environment

• Windows: env_name\Scripts\activate
• Linux/Mac: source env_name/bin/activate

Useful Libraries (Install with pip)

• NumPy: Numerical computing library.
• Pandas: Data manipulation and analysis library.
• Matplotlib: Data visualization library.
• Requests: HTTP library for making API requests.
• Beautiful Soup: HTML parsing library.
• SQLAlchemy: SQL toolkit and Object-Relational Mapping (ORM) library.

Remember, this cheat sheet is designed to provide a quick overview of Python 3 concepts and syntax. For more detailed explanations and examples, be sure to refer to the official Python documentation and other learning resources. Happy coding!