01 - Python Basics

📌 What You'll Learn

• •Python syntax and structure
• •Keywords and identifiers
• •Variables and data types
• •Input and output
• •Operators
• •Comments and indentation
• •Type casting
• •Math functions

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🔤 Python Syntax

Python is known for its clean and readable syntax. Unlike other languages, Python uses indentation (whitespace) to define code blocks instead of curly braces {}.

Key Points:

• •Python files have .py extension
• •Python is case-sensitive (Name ≠ name)
• •Statements end with a newline (no semicolon needed)
• •Use 4 spaces for indentation (standard)

# This is a valid Python program
print("Hello, World!")

# Indentation matters!
if True:
    print("This is indented")  # 4 spaces

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🔑 Keywords and Identifiers

Keywords

Reserved words that have special meaning in Python. You cannot use them as variable names.

# Python 3.10+ has 35 keywords:
False, None, True, and, as, assert, async, await,
break, class, continue, def, del, elif, else, except,
finally, for, from, global, if, import, in, is,
lambda, nonlocal, not, or, pass, raise, return,
try, while, with, yield

Identifiers

Names given to variables, functions, classes, etc.

Rules:

1. •Can contain letters (a-z, A-Z), digits (0-9), and underscore (_)
2. •Cannot start with a digit
3. •Cannot be a keyword
4. •Case-sensitive

# Valid identifiers
my_variable = 10
_private = 20
userName123 = "John"
MyClass = "class"

# Invalid identifiers
# 123abc = 10    ❌ Starts with digit
# my-var = 10    ❌ Contains hyphen
# class = 10     ❌ Is a keyword

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📦 Variables and Data Types

Variables

Variables are containers for storing data values. Python has no command for declaring variables - they are created when you assign a value.

# Variable assignment
name = "Alice"      # String
age = 25            # Integer
height = 5.6        # Float
is_student = True   # Boolean

# Multiple assignment
x, y, z = 1, 2, 3
a = b = c = 100     # Same value to multiple variables

Data Types

# Check type with type()
print(type(42))        # <class 'int'>
print(type(3.14))      # <class 'float'>
print(type("Hello"))   # <class 'str'>
print(type(True))      # <class 'bool'>

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🖥️ Input and Output

Output with print()

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

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

# Print with separator
print("a", "b", "c", sep="-")  # a-b-c

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

# Print with formatting
name = "Alice"
age = 25
print(f"Name: {name}, Age: {age}")  # f-string (recommended)

Input with input()

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

# Convert input to number
age = int(input("Enter your age: "))
height = float(input("Enter your height: "))

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➕ Operators

Arithmetic Operators

a, b = 10, 3

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

Comparison Operators

a, b = 10, 5

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

Logical Operators

x, y = True, False

print(x and y)  # False  Both must be True
print(x or y)   # True   At least one True
print(not x)    # False  Inverts the value

Assignment Operators

x = 10      # Assign
x += 5      # x = x + 5  → 15
x -= 3      # x = x - 3  → 12
x *= 2      # x = x * 2  → 24
x /= 4      # x = x / 4  → 6.0
x //= 2     # x = x // 2 → 3.0
x %= 2      # x = x % 2  → 1.0
x **= 3     # x = x ** 3 → 1.0

Bitwise Operators

a, b = 5, 3  # Binary: a=0101, b=0011

print(a & b)   # 1   AND (0001)
print(a | b)   # 7   OR (0111)
print(a ^ b)   # 6   XOR (0110)
print(~a)      # -6  NOT (inverts all bits)
print(a << 1)  # 10  Left shift (1010)
print(a >> 1)  # 2   Right shift (0010)

Identity Operators

a = [1, 2, 3]
b = [1, 2, 3]
c = a

print(a is c)      # True   Same object in memory
print(a is b)      # False  Different objects
print(a is not b)  # True
print(a == b)      # True   Same values (equality)

Membership Operators

fruits = ["apple", "banana", "cherry"]

print("apple" in fruits)      # True
print("mango" in fruits)      # False
print("mango" not in fruits)  # True

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💬 Comments and Indentation

Comments

# This is a single-line comment

# Multi-line comments using multiple #
# Line 1
# Line 2

"""
This is a multi-line string (docstring)
Often used as multi-line comments
But technically it's a string literal
"""

'''
Single quotes work too
for multi-line strings
'''

Indentation

# Python uses indentation to define code blocks
# Standard: 4 spaces (not tabs)

if True:
    print("Indented block")  # 4 spaces
    if True:
        print("Nested block")  # 8 spaces

# IndentationError if incorrect:
# if True:
# print("Error!")  # Not indented - ERROR!

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🔄 Type Casting

Converting one data type to another.

# String to Integer
age_str = "25"
age_int = int(age_str)  # 25

# String to Float
price_str = "19.99"
price_float = float(price_str)  # 19.99

# Number to String
num = 42
num_str = str(num)  # "42"

# Float to Integer (truncates decimal)
pi = 3.14159
pi_int = int(pi)  # 3

# Integer to Float
x = 10
x_float = float(x)  # 10.0

# To Boolean
print(bool(0))     # False
print(bool(1))     # True
print(bool(""))    # False (empty string)
print(bool("Hi"))  # True (non-empty string)
print(bool([]))    # False (empty list)
print(bool([1]))   # True (non-empty list)

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🔢 Math Functions

Built-in Math Functions

# Basic functions
print(abs(-10))      # 10  Absolute value
print(round(3.7))    # 4   Round to nearest integer
print(round(3.14159, 2))  # 3.14  Round to 2 decimals
print(pow(2, 3))     # 8   Power (2^3)
print(min(1, 5, 3))  # 1   Minimum
print(max(1, 5, 3))  # 5   Maximum
print(sum([1, 2, 3]))# 6   Sum of iterable
print(divmod(10, 3)) # (3, 1)  Quotient and remainder

Math Module

import math

# Constants
print(math.pi)      # 3.141592653589793
print(math.e)       # 2.718281828459045

# Functions
print(math.sqrt(16))    # 4.0  Square root
print(math.ceil(3.2))   # 4    Ceiling (round up)
print(math.floor(3.8))  # 3    Floor (round down)
print(math.factorial(5)) # 120  5!
print(math.gcd(12, 8))  # 4    Greatest common divisor
print(math.log(10))     # 2.302... Natural log
print(math.log10(100))  # 2.0  Log base 10
print(math.sin(math.pi/2))  # 1.0  Sine
print(math.cos(0))      # 1.0  Cosine
print(math.degrees(math.pi))  # 180.0  Radians to degrees
print(math.radians(180))  # 3.14159... Degrees to radians

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📝 Summary

• •Python uses clean syntax with indentation
• •Variables don't need type declarations
• •Python has various data types: int, float, str, bool, list, tuple, dict, set
• •Use input() for user input, print() for output
• •Multiple types of operators: arithmetic, comparison, logical, bitwise
• •Type casting converts between data types
• •Math module provides advanced mathematical functions

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🎯 Next Steps

After mastering these basics, proceed to 02_strings to learn about string manipulation!