Introduction to Python

What is Python?

Python is a high-level, interpreted programming language created by Guido van Rossum and first released in 1991. It emphasizes code readability and simplicity - its design philosophy is that there should be one obvious way to do things, and that code should be readable without needing extensive comments.

Python is dynamically typed (you do not declare variable types), garbage collected (memory is managed automatically), and supports multiple programming paradigms: procedural, object-oriented, and functional.

# Python is readable - this is nearly plain English
name = "Alice"
age  = 30

if age >= 18:
    print(f"{name} is an adult.")
else:
    print(f"{name} is a minor.")

# No semicolons, no braces, no type declarations
# Indentation defines code blocks

Why Python is Popular

Python has been the most popular programming language in the TIOBE Index and Stack Overflow surveys for several years. Several factors drive this:

• Readable syntax - code is close to pseudocode, lowering the barrier to entry
• Huge standard library - "batteries included" means most common tasks have a built-in solution
• Massive ecosystem - PyPI hosts over 500,000 packages covering every domain
• Dominance in AI/ML - PyTorch, TensorFlow, scikit-learn, pandas, and NumPy are all Python-first
• Versatility - the same language works for quick scripts, web APIs, data pipelines, and research
• Community - large, welcoming community with extensive documentation and tutorials

Key Use Cases

Python 3 vs Python 2

Python 2 reached end-of-life on January 1, 2020. All new code should use Python 3. The current stable series is Python 3.12 (as of 2024), with 3.13 in active development.

How Python Works

Python is an interpreted language. When you run a .py file, CPython (the reference implementation) compiles it to bytecode (.pyc files), then the Python Virtual Machine executes that bytecode. This happens transparently - you never manually compile Python code.

# Write your code in a .py file
$ python hello.py        # CPython compiles + runs it
$ python3 hello.py       # On systems with both Python 2 and 3

# Or use the interactive REPL (Read-Eval-Print Loop)
$ python3
>>> 2 + 2
4
>>> print("Hello")
Hello
>>> exit()

Python vs Other Languages

First Look at Python Code

# Variables - no type declarations needed
name    = "Alice"
age     = 30
height  = 1.75
is_admin = True

# Lists (like arrays)
fruits = ["apple", "banana", "cherry"]
print(fruits[0])   # apple
print(fruits[-1])  # cherry (negative index)

# Dictionaries (key-value pairs)
user = {"name": "Alice", "age": 30}
print(user["name"])  # Alice

# Functions
def greet(person):
    return f"Hello, {person}!"

print(greet("Bob"))  # Hello, Bob!

# Classes
class Dog:
    def __init__(self, name):
        self.name = name

    def bark(self):
        return f"{self.name} says woof!"

dog = Dog("Rex")
print(dog.bark())  # Rex says woof!

apple
cherry
Alice
Hello, Bob!
Rex says woof!