Python Type Conversion

What Is Type Conversion?

Type conversion means changing a value from one data type into another data type.

For example, a number stored as text can be converted into an integer:

age = "25"

age = int(age)

print(age)

25

Before conversion, age was a string. After conversion, it is an integer.

Why Is Type Conversion Needed?

Python treats different data types differently. Sometimes a value arrives in a type that is not suitable for the operation you want to perform.

A very common example is user input.

age = input("Enter your age: ")

print(type(age))

Enter your age: 25
<class 'str'>

Even though the user typed 25, Python receives it as a string.

If we want to perform mathematical calculations, we usually need to convert it first.

age = int(input("Enter your age: "))

print(age + 1)

Enter your age: 25
26

Implicit Type Conversion

Implicit conversion happens automatically. Python converts a value when necessary without you explicitly calling a conversion function.

A common example occurs when an integer and a floating-point number are used together.

number = 10
decimal = 2.5

result = number + decimal

print(result)
print(type(result))

12.5
<class 'float'>

Python automatically promotes the integer value to a floating-point value for the calculation.

Explicit Type Conversion

Explicit conversion is when you deliberately tell Python which type you want.

Python provides several built-in functions for this.

number = "50"

number = int(number)

print(number)
print(type(number))

50
<class 'int'>

Here, the programmer explicitly requested conversion using int().

Converting Values with int()

The int() function converts a compatible value into an integer.

String to Integer

age = int("25")

print(age)
print(type(age))

25
<class 'int'>

Float to Integer

number = int(3.9)

print(number)

3

For example, int(7.99) produces 7, not 8.

Converting Values with float()

The float() function converts a compatible value into a floating-point number.

price = float("19.99")

print(price)
print(type(price))

19.99
<class 'float'>

Integers can also be converted into floating-point values.

number = float(10)

print(number)

10.0

Converting Values with str()

The str() function converts a value into a string.

number = 100

text = str(number)

print(text)
print(type(text))

100
<class 'str'>

This is especially useful when combining numbers with text outside of formatted strings.

age = 25

message = "I am " + str(age) + " years old."

print(message)

I am 25 years old.

Converting Values with bool()

The bool() function converts a value into either True or False.

print(bool(1))
print(bool(0))

print(bool("hello"))
print(bool(""))

True
False
True
False

Common False Values

Several values are considered false-like in Python, including:

• False
• 0
• 0.0
• "" — empty string
• [] — empty list
• () — empty tuple
• {} — empty dictionary
• None

Most non-empty collections and non-zero numbers evaluate to True.

Converting Values with list()

The list() function can convert an iterable into a list.

String to List

letters = list("Python")

print(letters)

['P', 'y', 't', 'h', 'o', 'n']

Tuple to List

numbers = (10, 20, 30)

result = list(numbers)

print(result)

[10, 20, 30]

Converting Values with tuple()

The tuple() function converts an iterable into a tuple.

numbers = [1, 2, 3, 4]

result = tuple(numbers)

print(result)

(1, 2, 3, 4)

Remember that lists are mutable while tuples are immutable.

Converting Values with set()

The set() function converts an iterable into a set.

numbers = [1, 1, 2, 2, 3, 3]

unique_numbers = set(numbers)

print(unique_numbers)

{1, 2, 3}

Converting Values with dict()

The dict() function can create a dictionary from suitable key-value pairs.

pairs = [
    ("name", "Ali"),
    ("age", 25)
]

person = dict(pairs)

print(person)

{'name': 'Ali', 'age': 25}

Each pair contains a key followed by its corresponding value.

User Input and Type Conversion

One of the most important real-world uses of type conversion is handling user input.

The input() function always returns a string.

Example: Adding Two Numbers

first = input("Enter first number: ")
second = input("Enter second number: ")

result = int(first) + int(second)

print(result)

Enter first number: 15
Enter second number: 25
40

A Cleaner Approach

first = int(input("Enter first number: "))
second = int(input("Enter second number: "))

print(first + second)

Converting the input immediately makes the variable ready for mathematical operations.

Conversion Errors

Not every value can be converted into every data type. When a conversion is invalid, Python raises an error.

Invalid Integer Conversion

number = int("hello")

ValueError: invalid literal for int()

Python cannot interpret the word "hello" as an integer.

Invalid Float Conversion

price = float("Python")

This also produces a ValueError.

Common Type Conversion Mistakes

Mistake 1: Adding Strings Instead of Numbers

first = "10"
second = "20"

print(first + second)

1020

Python concatenates the strings instead of performing arithmetic.

Correct version:

first = "10"
second = "20"

print(int(first) + int(second))

30

Mistake 2: Expecting int() to Round

print(int(8.9))

8

int() truncates the decimal portion. It does not perform normal rounding.

Mistake 3: Forgetting That input() Returns a String

age = input("Age: ")

print(age + 5)

This causes a type error because Python cannot add an integer directly to a string.

Use:

age = int(input("Age: "))

print(age + 5)

Practice Exercises

print(int(9.99))
print(float("20"))
print(bool(0))
print(bool("Python"))

Mini Challenge

250.50 × 3 = 751.50

Quick Knowledge Check

Test what you have learned in this lesson.

Lesson Summary

Type conversion allows Python programs to change values from one data type into another.