Type Conversion

Learn how to convert values from one data type to another so Python can use them correctly in calculations, analysis, and output.

Skill Level: Beginner
Prerequisites: Variables, Data Types
Estimated Time: 20 minutes

Story Time

In the previous lesson, you learned that Python stores different kinds of information using different data types. However, real data is not always stored in the form we need.

For example, a number entered by a user may arrive as text. A value from a CSV file may look numeric but still be stored as a string. Before Python can calculate, compare, or analyze these values, we often need to convert them.

That process is called type conversion. It is an important skill because data analysis often begins with turning raw values into the correct format for computation.

What You’ll Learn

By the end of this lesson, you will be able to:

• Explain what type conversion is.
• Convert between common Python data types.
• Use built-in conversion functions such as int(), float(), str(), and bool().
• Recognize situations where type conversion is needed.
• Avoid common beginner mistakes when converting values.

What Is Type Conversion?

Type conversion is the process of changing a value from one data type into another.

For example:

age = "21"
print(type(age))

Output:

<class 'str'>

Even though "21" looks like a number, Python treats it as text because it is inside quotation marks.

Converting to an Integer

Use the int() function when you want to convert a value into a whole number.

age = "21"
age = int(age)

print(age)
print(type(age))

Output:

21
<class 'int'>

This is useful when a value should be treated as a count, age, or any other whole-number quantity.

Converting to a Float

Use the float() function when a value should be stored as a decimal number.

height = "172.5"
height = float(height)

print(height)
print(type(height))

Output:

172.5
<class 'float'>

This is common when working with measurements, averages, prices, and percentages.

Converting Numbers to Strings

Use the str() function to turn a number into text.

score = 95
score = str(score)

print(score)
print(type(score))

Output:

95
<class 'str'>

This is useful when you want to combine numbers with messages or labels in output.

Converting to a Boolean

Use the bool() function to convert a value into True or False.

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

Output:

True
False

Some common examples are:

Value	Result
bool(1)	True
bool(0)	False
bool("")	False
bool("Python")	True

In Python, many values have a truth value. Zero and empty strings are treated as False, while many other values are treated as True.

A Note About "True" and "False"

This is a common beginner confusion. The string "True" is still text, not a Boolean value.

For example:

print(bool("False"))

Output:

True

That happens because the string is not empty. In Python, a non-empty string converts to True, even if the text inside it says "False".

So if your data contains the text "True" or "False", you should not assume that bool() will interpret the meaning of the word. You may need to compare the string directly or clean it before conversion.

Common Conversion Functions

Function	Converts To
int()	Integer
float()	Float
str()	String
bool()	Boolean

These are the conversion functions you will use most often in beginner Python programs.

Worked Example

age = "22"
height = "168.5"

age = int(age)
height = float(height)

print(age)
print(height)

print(type(age))
print(type(height))

Output:

22
168.5
<class 'int'>
<class 'float'>

This example shows how text values can be converted into numeric values so they can be used properly in calculations.

Why Conversion Is Important

Consider this code:

age = input("Enter your age: ")
print(age + 5)

This produces an error because input() returns text, not a number.

Correct version:

age = int(input("Enter your age: "))
print(age + 5)

Now Python can perform numerical addition because the input has been converted to an integer.

Quick Check

Predict the output before running the code:

number = "50"

print(type(number))

number = int(number)

print(type(number))

This is a simple way to check whether you understand how conversion changes a value.

Practice in the Notebook

Notebook

Open in Google Colab

Practice this lesson in a live notebook.

After completing the activity in Google Colab, mark it as complete below.

Create the following variables as strings:

age = "20"
height = "170.2"

Convert them into the appropriate data types and display both the value and the type.

You can use this pattern:

age = "20"
height = "170.2"

age = int(age)
height = float(height)

print(age, type(age))
print(height, type(height))

Try It Yourself

Convert the following values:

price = "45.99"
students = "120"
marks = 88

Tasks:

• Convert price to a float.
• Convert students to an integer.
• Convert marks to a string.
• Display the data type after each conversion.

Challenge

A survey dataset contains the following values as text:

age = "24"
gpa = "3.85"
graduated = "True"

Convert each value into the most appropriate data type.

Then think carefully about graduated. Should "True" be converted using bool(), or should it be handled another way?

This is an important question because real datasets often contain text values that look like Boolean values but need extra cleaning before they can be used safely.

Common Mistakes

Trying to convert non-numeric text into an integer

number = "Python"
int(number)

This causes a ValueError because "Python" is not a numeric string.

Forgetting to store the converted value

Incorrect:

age = "20"
int(age)

print(type(age))

Output:

<class 'str'>

Correct:

age = int(age)
print(type(age))

Output:

<class 'int'>

The conversion must be assigned back to a variable if you want the change to be saved.

Assuming input() returns numbers

age = input("Age: ")

input() always returns a string, even when the user types digits.

If you want to do arithmetic with the result, convert it first.

Key Takeaways

• Type conversion changes a value from one data type into another.
• int(), float(), str(), and bool() are common Python conversion functions.
• input() returns a string, so conversion is often needed before calculations.
• Non-empty strings such as "False" can still convert to True with bool(), so Boolean-like text should be handled carefully.
• Type conversion is an essential skill for preparing data for analysis.

Self Evaluation

Check Your Understanding

1. What is type conversion?

Changing one data type into anotherDeleting a variable from memoryPrinting the value of a variableRenaming a function

2. Which function converts a string such as "21" into a whole number?

float()bool()int()str()

3. Why does `age = input("Enter your age: ")` often need conversion afterward?

Because `input()` returns a floatBecause `input()` always returns a stringBecause `input()` creates a BooleanBecause `input()` deletes spaces

4. What is the result of `bool("False")`?

`False``True`An error`0`

5. Which conversion is most appropriate for the string `"45.99"`?

`int()``float()``bool()``type()`

Continue Your Journey

In the next lesson, you will explore built-in functions, which will help you perform useful tasks more efficiently in Python.