Python Cheat Sheet: A Quick Guide to Core Syntax and Features

Key Takeaways

1. Python has simple, readable syntax ideal for beginners.
2. Core structures like lists, dictionaries, and loops are essential to master.
3. Understanding basic file handling and exceptions improves code robustness.

Python is a versatile and widely-used programming language known for its readability and efficiency. This cheat sheet provides a quick reference to essential Python concepts, syntax, and commands.

Basic Syntax

Printing Output

To display output in Python, use the print() function:

print("Hello, World!")

Comments

Use the # symbol to add comments in your code:

# This is a single-line comment

"""
This is a
multi-line comment.
"""

Variables and Data Types

Variables

Assign values to variables using the = operator:

message = "Hello, Python!"

Data Types

Common data types in Python include:

• Integer (int): Whole numbers, e.g., 42
• Float (float): Decimal numbers, e.g., 3.14
• String (str): Sequence of characters, e.g., "Python"
• Boolean (bool): True or False

Control Flow

Conditional Statements

Use if, elif, and else to execute code based on conditions:

x = 10
if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")

Loops

For Loop

Iterate over a sequence (like a list or range):

for i in range(5):
    print(i)

While Loop

Execute a block of code as long as a condition is true:

count = 0
while count < 5:
    print(count)
    count += 1

Functions

Define reusable blocks of code using functions:

def greet(name):
    return f"Hello, {name}!"

print(greet("Alice"))

Data Structures

Lists

Ordered, mutable collections:

fruits = ["apple", "banana", "cherry"]
fruits.append("date")  # Adds "date" to the list

Tuples

Ordered, immutable collections:

coordinates = (4, 5)

Dictionaries

Unordered collections of key-value pairs:

person = {"name": "Alice", "age": 30}
print(person["name"])  # Outputs: Alice

Sets

Unordered collections of unique elements:

unique_numbers = {1, 2, 3, 3, 4}
print(unique_numbers)  # Outputs: {1, 2, 3, 4}

File Handling

Read from and write to files using the open() function:

# Writing to a file
with open("example.txt", "w") as file:
    file.write("Hello, File!")

# Reading from a file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

Exception Handling

Manage errors gracefully using try and except blocks:

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

This cheat sheet covers fundamental aspects of Python programming. For more detailed information, consider exploring official Python documentation and other comprehensive resources.

FAQs

What is the best way to comment code in Python?

Use # for single-line comments and triple quotes (""") for multi-line explanations.

How do I define a function in Python?

Use the def keyword followed by the function name and parameters.

What data structures should I learn first?

Start with lists, dictionaries, tuples, and sets for foundational knowledge.

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