# String to integer
age_str = "25"
age = int(age_str)      # 25

# Float to integer (removes decimal)
price = 9.99
whole = int(price)      # 9

# User input (always a string!)
num = int(input("Enter number: "))

Warning: int("hello") causes an error! Only numeric strings can be converted.

`float()`

Converts to float (decimal number)

# String to float
price_str = "19.99"
price = float(price_str) # 19.99

# Integer to float
count = 5
decimal = float(count)   # 5.0

# Division result
result = float(7) / 2   # 3.5

`str()`

Converts to string (text)

# Integer to string
age = 15
age_text = str(age)      # "15"

# Float to string
price = 9.99
price_text = str(price)  # "9.99"

# Concatenating with strings
print("Age: " + str(age))  # "Age: 15"

`bool()`

Converts to boolean (True/False)

# Numbers to boolean
bool(0)      # False (zero)
bool(1)      # True (non-zero)
bool(-5)     # True (non-zero)

# Strings to boolean
bool("")     # False (empty)
bool("hi")   # True (non-empty)
bool("False") # True (non-empty string!)

Why Do We Need Casting?

User Input is Always a String

# This won't work as expected!
age = input("Enter age: ")  # "25" (string)
if age > 18:                # ERROR! Can't compare string to int

# Fix: Convert to integer first
age = int(input("Enter age: "))  # 25 (integer)
if age > 18:                     # Works!

Combining Text and Numbers

# This causes a TypeError!
score = 95
print("Score: " + score)     # ERROR!

# Fix 1: Convert to string
print("Score: " + str(score)) # "Score: 95"

# Fix 2: Use f-string (recommended)
print(f"Score: {score}")     # "Score: 95"

Key Vocabulary

data type

The category of data a value belongs to. Determines what operations you can perform.

string (str)

Text data, written in quotes. "Hello", 'Python', "123"

integer (int)

A whole number with no decimal. 42, -7, 0

float

A decimal number. 3.14, -0.5, 2.0

boolean (bool)

True or False values. True, False

casting

Converting data from one type to another. Also called type conversion.

int()

Converts a value to an integer. int("5") gives 5

str()

Converts a value to a string. str(42) gives "42"

float()

Converts a value to a float. float("3.14") gives 3.14

Quick Reference

data_types_examples.py

# String - text in quotes
name = "Alice"
message = 'Hello World'

# Integer - whole numbers
age = 15
score = -10

# Float - decimal numbers
price = 9.99
temperature = -2.5

# Boolean - True or False
is_student = True
has_passed = False

# Check data type
print(type(name))    # <class 'str'>
print(type(age))     # <class 'int'>
print(type(price))   # <class 'float'>

# Type conversion
num_str = "42"
num_int = int(num_str)    # String to integer
num_float = float(num_str) # String to float
back_to_str = str(42)     # Integer to string