2.4 Type Conversion

Introduction

Python provides the flexibility to convert data from one type to another. This process is called type conversion or type casting. Understanding type conversion is essential because data in real-world applications often comes in different forms (e.g., user input is typically received as a string and may need to be converted into an integer for mathematical operations).

This section covers:

• Implicit type conversion (automatic conversion by Python)
• Explicit type conversion (manual conversion using functions like int(), float(), str(), and bool())
• Common use cases for type conversion

By the end of this lesson, you will be able to convert between different data types and avoid common conversion errors.

2.4.1 Implicit Type Conversion (Automatic by Python)

Python automatically converts one data type into another when necessary, which is known as implicit conversion. This typically happens when performing operations involving mixed data types.

Example: Integer to Float Conversion

num_int = 10      # Integer
num_float = 2.5   # Float
result = num_int + num_float  

print(result)      # Output: 12.5
print(type(result))  # Output: <class 'float'>

Python automatically converts the integer 10 into a float (10.0) before performing the addition, ensuring that the result is also a float.

Example: Integer to Boolean Conversion

num = 0  
print(bool(num))  # Output: False

num = 5  
print(bool(num))  # Output: True

In Python, 0 is considered False, while any nonzero number is considered True when converted to a Boolean.

2.4.2 Explicit Type Conversion (Manual Conversion)

Explicit type conversion (also known as type casting) is when the programmer manually converts one data type into another using built-in functions.

Common Type Conversion Functions in Python

2.4.3 Converting Strings to Integers and Floats

Strings that contain numeric values can be converted into integers or floats.

Example: Converting a Numeric String to an Integer

num_str = "25"  # This is a string
num_int = int(num_str)  # Convert to integer

print(num_int)   # Output: 25
print(type(num_int))  # Output: <class 'int'>

If a string contains only numeric characters, int() will successfully convert it into an integer.

Example: Converting a Numeric String to a Float

num_str = "12.34"
num_float = float(num_str)  # Convert to float

print(num_float)   # Output: 12.34
print(type(num_float))  # Output: <class 'float'>

A string containing decimal values can be converted into a float using float().

Handling Invalid Conversions

If a string contains non-numeric characters, attempting to convert it to an integer or float will result in an error.

num_str = "hello"
num_int = int(num_str)  # This will raise an error

Error Output:

ValueError: invalid literal for int() with base 10: 'hello'

To prevent this, always validate or check the input before conversion.

2.4.4 Converting Integers and Floats to Strings

When you need to concatenate numbers with strings, you must convert them to strings first.

Example: Integer to String

age = 25
message = "I am " + str(age) + " years old."

print(message)  # Output: I am 25 years old.

Example: Float to String

pi = 3.14159
print("The value of pi is " + str(pi))

Without str(), Python would raise a TypeError because it does not allow string concatenation with numbers.

2.4.5 Converting Between Booleans and Other Data Types

Example: Converting Integers to Boolean

print(bool(0))  # Output: False
print(bool(1))  # Output: True
print(bool(-5))  # Output: True

Any nonzero number is treated as True, while 0 is treated as False.

Example: Converting Strings to Boolean

print(bool(""))  # Output: False (empty string)
print(bool("Hello"))  # Output: True

An empty string evaluates to False, while any non-empty string evaluates to True.

Example: Converting Lists to Boolean

print(bool([]))  # Output: False (empty list)
print(bool([1, 2, 3]))  # Output: True

An empty list evaluates to False, while a non-empty list evaluates to True.

2.4.6 Real-World Use Cases of Type Conversion

Type conversion is frequently used in real-world applications, such as:

1. Processing User Input
   User input in Python is always received as a string, so conversion is required for numeric operations.

age = input("Enter your age: ")  # Always returns a string
age = int(age)  # Convert to integer
print("Next year, you will be", age + 1)

2. Reading Data from Files or APIs
   Data from files or APIs is usually in string format and often needs conversion.

data = "45.6"
temperature = float(data)  # Convert to float

3. Mathematical Calculations
   Converting float values to integers when necessary.

price = 19.99
discount_price = int(price)  # Convert float to integer

2.4.7 Summary

This section has discussed the following concepts:

• Implicit conversion happens automatically when Python promotes a lower data type (e.g., int to float).
• Explicit conversion requires functions like int(), float(), str(), and bool().
• Converting strings to numbers is useful when working with user input.
• Converting numbers to strings is necessary for text formatting.
• Boolean conversions help evaluate conditions in Python.

Understanding type conversion helps prevent errors and allows data manipulation in real-world applications.

What’s Next?

In the next lesson, 2.5 Input and Output in Python, you will learn how to take user input and display output using formatted text.