Python Basics

Python Programming

Python Basics

Beginner Lesson 2 of 10

Python Basics

In this lesson, we’ll explore the fundamental building blocks of Python: variables, data types, and operators.

Variables

Variables are containers for storing data values. In Python, you don’t need to declare a variable type - Python figures it out automatically.

# Creating variables
name = "Alice"
age = 25
height = 5.7
is_student = True

# Printing variables
print(name)        # Output: Alice
print(age)         # Output: 25
print(height)      # Output: 5.7
print(is_student)  # Output: True

Variable Naming Rules

• Must start with a letter or underscore
• Can contain letters, numbers, and underscores
• Case-sensitive (name and Name are different)
• Cannot use reserved keywords (if, for, class, etc.)

# Good variable names
user_name = "Bob"
userAge = 30
_private = "secret"
MAX_SIZE = 100

# Bad variable names (will cause errors)
# 2name = "Error"     # Cannot start with number
# my-name = "Error"   # Cannot use hyphens
# class = "Error"     # Cannot use reserved words

Python Naming Conventions

# snake_case for variables and functions (recommended)
first_name = "John"
total_count = 42

# UPPER_CASE for constants
MAX_CONNECTIONS = 100
PI = 3.14159

# PascalCase for classes
class UserProfile:
    pass

Data Types

Python has several built-in data types:

Numeric Types

# Integer (int) - whole numbers
count = 42
negative = -10
big_number = 1_000_000  # Underscores for readability

# Float - decimal numbers
price = 19.99
temperature = -5.5
scientific = 1.5e-4  # Scientific notation (0.00015)

# Complex numbers
complex_num = 3 + 4j

Strings

# Strings - text data
single_quotes = 'Hello'
double_quotes = "World"
multiline = """This is a
multiline string"""

# String operations
greeting = "Hello"
name = "World"
message = greeting + " " + name  # Concatenation: "Hello World"
repeated = "Ha" * 3              # Repetition: "HaHaHa"

# String indexing (0-based)
text = "Python"
print(text[0])    # 'P' (first character)
print(text[-1])   # 'n' (last character)
print(text[0:3])  # 'Pyt' (slicing)

# Useful string methods
text = "  hello world  "
print(text.upper())      # "  HELLO WORLD  "
print(text.lower())      # "  hello world  "
print(text.strip())      # "hello world"
print(text.replace("world", "Python"))  # "  hello Python  "
print(len(text))         # 15

# f-strings (formatted strings) - Python 3.6+
name = "Alice"
age = 25
print(f"My name is {name} and I'm {age} years old")

Booleans

# Boolean - True or False
is_active = True
is_logged_in = False

# Boolean operations
print(True and False)   # False
print(True or False)    # True
print(not True)         # False

# Truthy and Falsy values
# Falsy: False, 0, 0.0, "", [], {}, None
# Truthy: Everything else

None Type

# None represents absence of value
result = None

if result is None:
    print("No result yet")

Type Checking and Conversion

# Check type
x = 42
print(type(x))  # <class 'int'>

y = "hello"
print(type(y))  # <class 'str'>

# Type conversion (casting)
num_str = "42"
num_int = int(num_str)    # String to integer: 42
num_float = float(num_str) # String to float: 42.0

num = 42
num_as_str = str(num)     # Integer to string: "42"

# Be careful with invalid conversions
# int("hello")  # ValueError!

Operators

Arithmetic Operators

a = 10
b = 3

print(a + b)   # Addition: 13
print(a - b)   # Subtraction: 7
print(a * b)   # Multiplication: 30
print(a / b)   # Division: 3.333...
print(a // b)  # Floor division: 3
print(a % b)   # Modulus (remainder): 1
print(a ** b)  # Exponentiation: 1000

Comparison Operators

a = 10
b = 5

print(a == b)   # Equal: False
print(a != b)   # Not equal: True
print(a > b)    # Greater than: True
print(a < b)    # Less than: False
print(a >= b)   # Greater or equal: True
print(a <= b)   # Less or equal: False

Logical Operators

x = True
y = False

print(x and y)  # False (both must be True)
print(x or y)   # True (at least one True)
print(not x)    # False (negation)

# Practical example
age = 25
has_license = True

can_drive = age >= 18 and has_license
print(can_drive)  # True

Assignment Operators

x = 10       # Assign
x += 5       # Add and assign (x = x + 5) → 15
x -= 3       # Subtract and assign → 12
x *= 2       # Multiply and assign → 24
x /= 4       # Divide and assign → 6.0
x //= 2      # Floor divide and assign → 3.0
x **= 2      # Power and assign → 9.0
x %= 4       # Modulus and assign → 1.0

User Input

# Getting input from user
name = input("What is your name? ")
print(f"Hello, {name}!")

# Input is always a string - convert if needed
age_str = input("Enter your age: ")
age = int(age_str)  # Convert to integer
birth_year = 2024 - age
print(f"You were born around {birth_year}")

Practice Exercises

Exercise 1: Variable Swap

Swap the values of two variables without using a third variable.

# Your task: Swap a and b
a = 5
b = 10
# After swap: a should be 10, b should be 5

Solution

a = 5
b = 10
a, b = b, a  # Python's tuple unpacking!
print(a, b)  # 10, 5

Exercise 2: Temperature Converter

Convert temperature from Celsius to Fahrenheit.

# Formula: F = (C × 9/5) + 32
celsius = 25
# Calculate fahrenheit

Solution

celsius = 25
fahrenheit = (celsius * 9/5) + 32
print(f"{celsius}°C = {fahrenheit}°F")  # 25°C = 77.0°F

Exercise 3: String Manipulation

Given a user’s full name, extract and print the initials.

full_name = "John Michael Smith"
# Output should be: J.M.S.

Solution

full_name = "John Michael Smith"
parts = full_name.split()
initials = ".".join([name[0] for name in parts]) + "."
print(initials)  # J.M.S.

Summary

In this lesson, you learned:

• ✅ How to create and name variables
• ✅ Python’s main data types (int, float, str, bool, None)
• ✅ Type checking and conversion
• ✅ Arithmetic, comparison, logical, and assignment operators
• ✅ Getting user input

Next Steps

In the next lesson, we’ll explore data structures in Python:

• Lists, Tuples, and Sets
• Dictionaries
• Common operations on collections

Continue to Data Types →