Python Basics - Getting Started with Python

# Check Python version
python --version
# Output: Python 3.11.0 (or similar)

# Run Python interactively
python
# This opens Python REPL (Read-Eval-Print Loop)

After installation, verify Python is working by checking the version. You can also run Python interactively.

# This is a comment
print("Hello, World!")

# Run this file with: python hello.py

The `print()` function displays output. Comments start with `#`. Save this as a `.py` file and run it.

# String variable
name = "Alice"
print(name)  # Output: Alice

# Integer variable
age = 25
print(age)  # Output: 25

# Float (decimal) variable
height = 5.6
print(height)  # Output: 5.6

# Boolean variable
is_student = True
print(is_student)  # Output: True

Variables are created by assigning values. Python automatically determines the data type.

# String (str)
text = "Hello, Python!"
print(type(text))  # <class 'str'>

# Integer (int)
number = 42
print(type(number))  # <class 'int'>

# Float (float)
decimal = 3.14
print(type(decimal))  # <class 'float'>

# Boolean (bool)
is_active = True
print(type(is_active))  # <class 'bool'>

# List (list)
fruits = ["apple", "banana", "orange"]
print(type(fruits))  # <class 'list'>

# Dictionary (dict)
person = {"name": "Alice", "age": 25}
print(type(person))  # <class 'dict'>

Use `type()` to check the data type of a variable. Python has several built-in data types.

# Basic print
print("Hello, World!")

# Print multiple values
name = "Alice"
age = 25
print("Name:", name, "Age:", age)

# Formatted strings (f-strings) - Python 3.6+
print(f"Name: {name}, Age: {age}")

# Print with separator
print("Python", "is", "awesome", sep="-")  # Output: Python-is-awesome

# Print without newline
print("Hello", end=" ")
print("World")  # Output: Hello World

The `print()` function is versatile. You can print multiple values, use f-strings for formatting, and control separators and endings.

# Get user input
name = input("Enter your name: ")
print(f"Hello, {name}!")

# Input always returns a string
age = input("Enter your age: ")
print(type(age))  # <class 'str'>

# Convert input to number
age = int(input("Enter your age: "))
print(f"You are {age} years old")
print(type(age))  # <class 'int'>

The `input()` function gets user input. It always returns a string, so convert to numbers when needed using `int()` or `float()`.

# Addition
result = 10 + 5
print(result)  # 15

# Subtraction
result = 10 - 5
print(result)  # 5

# Multiplication
result = 10 * 5
print(result)  # 50

# Division (always returns float)
result = 10 / 5
print(result)  # 2.0

# Floor division (integer division)
result = 10 // 3
print(result)  # 3

# Modulus (remainder)
result = 10 % 3
print(result)  # 1

# Exponentiation (power)
result = 2 ** 3
print(result)  # 8

Python supports all standard arithmetic operations. Division always returns a float, use `//` for integer division.

x = 10
y = 5

print(x == y)  # False (equal)
print(x != y)  # True (not equal)
print(x > y)   # True (greater than)
print(x < y)   # False (less than)
print(x >= y)  # True (greater than or equal)
print(x <= y)  # False (less than or equal)

Comparison operators return boolean values (True or False).

a = True
b = False

print(a and b)  # False
print(a or b)   # True
print(not a)    # False

Logical operators work with boolean values: `and`, `or`, and `not`.

# String concatenation
first_name = "Alice"
last_name = "Smith"
full_name = first_name + " " + last_name
print(full_name)  # Alice Smith

# String repetition
greeting = "Hello! " * 3
print(greeting)  # Hello! Hello! Hello!

# String methods
text = "  Python Programming  "
print(text.strip())        # Remove whitespace
print(text.upper())        # Uppercase
print(text.lower())        # Lowercase
print(text.replace("Python", "Java"))  # Replace

# String formatting
name = "Alice"
age = 25
message = f"My name is {name} and I'm {age} years old"
print(message)

Python provides many string operations. F-strings (formatted string literals) are the modern way to format strings.

# Get user information
print("=== Personal Information Form ===")
name = input("Enter your name: ")
age = int(input("Enter your age: "))
city = input("Enter your city: ")

# Process and display
print(f"\nHello, {name}!")
print(f"You are {age} years old.")
print(f"You live in {city}.")

# Calculate years until 100
years_to_100 = 100 - age
print(f"You will be 100 years old in {years_to_100} years!")

This complete program demonstrates input, variables, type conversion, and formatted output.