1. Basics: Variables, Data Types, and Input/Output

Code Example: Hello World, Variables, and Input

# Print a greeting
print("Hello, Python!")

# Assigning variables
name = "Alice"
age = 25
height = 5.4  # Float

# Input from the user
user_name = input("Enter your name: ")
print(f"Hello, {user_name}! Welcome to Python.")

Key Concepts

• Variables store data. Types: int, float, str, bool, etc.
• Use input() to take input and print() for output.
• String Interpolation: f"..." for formatted strings.

2. Conditional Statements

Code Example: If/Else

# A simple grading system
score = int(input("Enter your score: "))

if score >= 90:
    print("Grade: A")
elif score >= 75:
    print("Grade: B")
elif score >= 60:
    print("Grade: C")
else:
    print("Grade: F")

Key Concepts

• if, elif, else: Python uses indentation (not braces!) to define blocks.
• Conditions use comparison operators: ==, !=, <, >, <=, >=.

3. Loops

Code Example: For and While

# For loop example
for i in range(1, 6):  # Loops from 1 to 5
    print(f"Count: {i}")

# While loop example
counter = 5
while counter > 0:
    print(f"Countdown: {counter}")
    counter -= 1

Key Concepts

• range(start, stop, step): Generates numbers for loops.
• Loops simplify repetitive tasks.

4. Functions

Code Example: Functions and Return Values

# Function to calculate factorial
def factorial(n):
    if n == 0 or n == 1:
        return 1
    return n * factorial(n - 1)

print(f"Factorial of 5 is {factorial(5)}")

Key Concepts

• Functions organize reusable logic with def.
• Recursion: A function calls itself to solve smaller subproblems.

5. Lists and Dictionaries

Code Example: Lists

# Create and manipulate a list
fruits = ["apple", "banana", "cherry"]
fruits.append("orange")  # Add an element
print(fruits[1])  # Access by index
print(len(fruits))  # Length of the list

Code Example: Dictionaries

# Create and use a dictionary
person = {"name": "Alice", "age": 25, "city": "New York"}
print(person["name"])
person["age"] = 26  # Update a value
print(person)

Key Concepts

• Lists: Ordered, mutable collections (like arrays).
• Dictionaries: Key-value pairs for fast lookups.

6. Classes and OOP

Code Example: Object-Oriented Programming

# Define a class
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

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

# Create an object
my_dog = Dog("Buddy", 3)
print(my_dog.bark())

Key Concepts

• Classes model real-world entities.
• __init__: Constructor to initialize objects.

7. File Handling

Code Example: Read/Write Files

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

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

Key Concepts

• Use with open() to handle files. It automatically closes the file.

8. Error Handling

Code Example: Try/Except

# Handle errors gracefully
try:
    number = int(input("Enter a number: "))
    print(f"Square: {number ** 2}")
except ValueError:
    print("That's not a valid number!")

Key Concepts

• Handle runtime errors using try and except.

9. Libraries and Modules

Code Example: Using Built-in and Third-Party Modules

# Import math module
import math
print(math.sqrt(16))  # Square root

# Install and use third-party library (e.g., requests)
# pip install requests
import requests
response = requests.get("https://api.github.com")
print(response.status_code)

Key Concepts

• Standard library provides many utilities.
• Use pip to install third-party libraries.

10. Advanced Topics

List Comprehensions

# Quick way to create lists
squares = [x ** 2 for x in range(1, 6)]
print(squares)

Lambda Functions

# Anonymous functions
add = lambda x, y: x + y
print(add(3, 5))

Decorators

# Add functionality to functions
def log(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__}")
        return func(*args, **kwargs)
    return wrapper

@log
def greet(name):
    print(f"Hello, {name}!")

greet("Alice")

11. Generators

Code Example: Efficient Iteration

# Generator for Fibonacci numbers
def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b

for num in fibonacci(10):
    print(num)

Key Concepts

• Generators: Functions that yield values one at a time using yield, instead of returning them all at once.
• Saves memory compared to building large lists.

12. Iterators

Code Example: Custom Iterator

class Counter:
    def __init__(self, start, end):
        self.current = start
        self.end = end

    def __iter__(self):
        return self

    def __next__(self):
        if self.current > self.end:
            raise StopIteration
        self.current += 1
        return self.current - 1

counter = Counter(1, 5)
for num in counter:
    print(num)

Key Concepts

• Define __iter__() and __next__() to make objects iterable.
• Use StopIteration to end iteration.

13. Context Managers

Code Example: Custom Context Manager

class FileManager:
    def __init__(self, filename, mode):
        self.filename = filename
        self.mode = mode

    def __enter__(self):
        self.file = open(self.filename, self.mode)
        return self.file

    def __exit__(self, exc_type, exc_value, traceback):
        self.file.close()

with FileManager("example.txt", "w") as file:
    file.write("Hello, Context Manager!")

Key Concepts

• Automate resource management with __enter__ and __exit__.
• Useful for files, database connections, etc.

14. Python’s collections Module

Code Example: Defaultdict and Counter

from collections import defaultdict, Counter

# defaultdict example
dd = defaultdict(int)
dd["a"] += 1
print(dd)  # Output: defaultdict(<class 'int'>, {'a': 1})

# Counter example
words = ["apple", "banana", "apple"]
count = Counter(words)
print(count)  # Output: Counter({'apple': 2, 'banana': 1})

Key Features

• defaultdict: Provides default values for missing keys.
• Counter: Counts occurrences of items in a collection.

15. Functional Programming

Code Example: Map, Filter, Reduce

from functools import reduce

# Map: Apply function to each element
squares = list(map(lambda x: x**2, range(5)))
print(squares)  # Output: [0, 1, 4, 9, 16]

# Filter: Keep elements meeting a condition
evens = list(filter(lambda x: x % 2 == 0, range(5)))
print(evens)  # Output: [0, 2, 4]

# Reduce: Aggregate values
product = reduce(lambda x, y: x * y, range(1, 5))
print(product)  # Output: 24

Key Concepts

• Functional programming enables concise, expressive operations.

16. Python’s itertools Module

Code Example: Infinite Iterators

import itertools

# Infinite iterator
counter = itertools.count(start=1, step=2)
for num in itertools.islice(counter, 5):
    print(num)  # Output: 1, 3, 5, 7, 9

Key Features

• count(), cycle(), and repeat() for infinite iterators.
• combinations() and permutations() for advanced combinatorics.

17. Regular Expressions

Code Example: Matching Patterns

import re

text = "My phone number is 123-456-7890."
pattern = r"\d{3}-\d{3}-\d{4}"

match = re.search(pattern, text)
if match:
    print(match.group())  # Output: 123-456-7890

Key Concepts

• re.search(): Finds the first match.
• re.findall(): Returns all matches as a list.

18. Python’s os and sys Modules

Code Example: File and Directory Operations

import os

# List files in the current directory
print(os.listdir())

# Create a new directory
os.mkdir("new_folder")

Code Example: Command-Line Arguments

import sys

# Print command-line arguments
print(sys.argv)  # Output: List of arguments passed to the script

19. Python’s json Module

Code Example: JSON Serialization

import json

# Serialize
data = {"name": "Alice", "age": 25}
json_data = json.dumps(data)
print(json_data)  # Output: '{"name": "Alice", "age": 25}'

# Deserialize
parsed_data = json.loads(json_data)
print(parsed_data["name"])  # Output: Alice

Key Concepts

• Use json.dumps() to convert Python objects to JSON.
• Use json.loads() to parse JSON strings.

20. Asynchronous Programming with asyncio

Code Example: Async Functions

import asyncio

async def greet():
    print("Hello")
    await asyncio.sleep(1)
    print("World")

asyncio.run(greet())

Key Concepts

• Use async def to define asynchronous functions.
• Use await to pause execution.

21. Python’s dataclasses Module

Code Example: Simplified Data Models

from dataclasses import dataclass

@dataclass
class Person:
    name: str
    age: int

person = Person("Alice", 25)
print(person)  # Output: Person(name='Alice', age=25)

Key Concepts

• Reduces boilerplate for creating classes.
• Supports immutability with frozen=True.

22. Best Practices

1. Use Type Annotations:

   def add(a: int, b: int) -> int:
       return a + b
   

2. Follow PEP 8:

   • Use meaningful variable names.
   • Limit lines to 79 characters.

3. Write Unit Tests:

   import unittest
   
   class TestMath(unittest.TestCase):
       def test_add(self):
           self.assertEqual(add(2, 3), 5)
   

4. Handle Exceptions Gracefully:

   • Avoid bare except.

Resources

1. Python Official Docs
2. Real Python
3. PEP 8 Style Guide