Variables and Basic Data Types

Variables are labels assigned to values, serving as references to specific data.

Variable Naming Conventions

• Consist of letters, numbers, and underscores
• Cannot start with a number
• Case-sensitive
• Avoid Python keywords and function names
• Use descriptive, concise names
• Prefer lowercase lettters (avoid 'l' and 'O' due to visual ambiguity)

Strings

Strings are sequences of characters anclosed in single or double quotes.

String Case Modification

name = "ada lovelace"
print(name.title())   # Ada Lovelace
print(name.upper())   # ADA LOVELACE
print(name.lower())   # ada lovelace

String Interpolation

Python 3.6+ f-strings:

first = 'ada'
last = 'lovelace'
full = f'{first} {last}'
print(full)  # ada lovelace

Pre-3.6 format method:

full = '{} {}'.format(first, last)

String Operations

# Concatenation
combined = first + ' ' + last

# Whitespace removal
language = '  python  '
print(language.lstrip())  # 'python  '
print(language.rstrip())  # '  python'
print(language.strip())   # 'python'

# String replacement
message = "I really like dogs. My dog names Jack."
message = message.replace('dog', 'cat')
print(message)  # I really like cats. My cat names Jack.

# String splitting
words = "hello world python".split()
print(words)  # ['hello', 'world', 'python']

# Character counting
text = 'programming'
print(text.count('m'))  # 2

Numbers

# Basic operations
result = 3 ** 3  # 27 (exponentiation)
quotient = 10 // 3  # 3 (floor division)

# Large number formatting
universe_age = 14_000_000_000

# Type conversion
age = 23
message = "Happy " + str(age) + "rd Birthday!"

Multiple Assignment

x, y, z = 0, 0, 0

Constants

While Python lacks built-in constants, convention uses uppercase for constant-like variables:

MAX_CONNECTIONS = 5000

Lists

Lists are ordered collections enclosed in square brackets.

List Operations

# Creation and access
vehicles = ['car', 'bike', 'bus']
print(vehicles[0])    # car
print(vehicles[-1])   # bus

# Adding elements
vehicles.append('train')
vehicles.insert(1, 'plane')

# Removing elements
del vehicles[0]
removed = vehicles.pop()
vehicles.remove('bike')

# List organization
numbers = [3, 1, 4, 2]
numbers.sort()
numbers.reverse()
print(len(numbers))  # 4

List Slicing and Copying

items = ['a', 'b', 'c', 'd', 'e']
print(items[1:4])     # ['b', 'c', 'd']
copy_items = items[:]  # Creates a copy

List Comprehensions

squares = [x**2 for x in range(1, 6)]
print(squares)  # [1, 4, 9, 16, 25]

Tuples

Immutable sequences enclosed in parentheses:

dimensions = (200, 50)
# dimensions[0] = 250  # Error - tuples are immutable

Control Structures

If Statements

numbers = [1, 2, 3, 4]
for num in numbers:
    if num % 2 == 0:
        print(f'{num} is even')
    else:
        print(f'{num} is odd')

While Loops

count = 5
while count > 0:
    print(count)
    count -= 1

Dictionaries

Key-value pair collections enclosed in curly braces.

Dictionary Operations

# Creation and access
student = {'name': 'Alice', 'age': 20, 'grade': 'A'}
print(student['name'])  # Alice

# Adding and modifying
student['major'] = 'Computer Science'
student['age'] = 21

# Removing
removed_grade = student.pop('grade')

Dictionary Iteration

for key, value in student.items():
    print(f'{key}: {value}')

for key in student.keys():
    print(key)

for value in student.values():
    print(value)

Functions

Function Definition

def greet_person(name):
    """Display a greeting message"""
    return f'Hello, {name}!'

print(greet_person('Bob'))  # Hello, Bob!

Function Parameters

# Default parameters
def describe_pet(name, animal='dog'):
    return f'I have a {animal} named {name}'

# Variable arguments
def make_sandwich(*ingredients):
    return f'Sandwich with: {ingredients}'

# Keyword arguments
def build_profile(**info):
    return info

Classes

Class Definition

class Dog:
    def __init__(self, name, breed):
        self.name = name
        self.breed = breed
    
    def bark(self):
        return f'{self.name} says woof!'

my_dog = Dog('Rex', 'German Shepherd')
print(my_dog.bark())  # Rex says woof!

Inheritance

class Puppy(Dog):
    def __init__(self, name, breed, age):
        super().__init__(name, breed)
        self.age = age

File Operations

Reading Files

with open('data.txt') as file:
    content = file.read()
    
with open('data.txt') as file:
    for line in file:
        print(line.strip())

Writting Files

with open('output.txt', 'w') as file:
    file.write('Hello, World!\n')

Error Handling

try:
    result = 10 / 0
except ZeroDivisionError:
    print('Cannot divide by zero')
else:
    print('Division successful')

Testing

import unittest

def add_numbers(a, b):
    return a + b

class TestMath(unittest.TestCase):
    def test_addition(self):
        self.assertEqual(add_numbers(2, 3), 5)

if __name__ == '__main__':
    unittest.main()