Python Course #6: Type Conversion - Converting Between Data Types

Lesson 6 of 30

Type Conversion - Converting Between Data Types

Sometimes you need to convert data from one type to another. Python provides built-in functions to convert between different data types.

Converting to Integer - int()

The int() function converts a value to an integer (whole number).

# Converting string to integer
age_text = "25"
age = int(age_text)
print(age + 5) # Now we can do math!

Output:
30

Important: int() removes any decimal part:

price = int(9.99)
print(price) # Becomes 9, not 10

Output:
9

Q1: What does int(7.8) return?

A) 7

B) 8

C) 7.8

Converting to Float - float()

The float() function converts a value to a floating-point number (decimal).

# Converting string to float
height = float("5.9")
print(height * 2)

Output:
11.8

You can also convert integers to floats:

count = float(42)
print(count) # 42.0

Output:
42.0

Q2: Why do we need type conversion?

A) To make code look prettier

B) To perform operations that require specific data types

C) Python requires it for all variables

Converting to String - str()

The str() function converts a value to a string (text).

# Converting number to string
score = 95
message = "Your score is " + str(score)
print(message)

Output:
Your score is 95

Why? Because you cannot directly concatenate (join) strings and numbers:

# This would cause an error:
# print("I am " + 25 + " years old")

# Correct way:
print("I am " + str(25) + " years old")

Q3: What happens when you try to add a string and a number without conversion?

A) Python automatically converts them

B) You get an error

C) The number becomes 0

Common Conversion Errors

Be careful! Not all conversions work:

• int("hello") - ERROR! Cannot convert text to a number
• int("3.14") - ERROR! Use float() first, then int()
• float("twenty") - ERROR! Must be a number in text form

Practice Challenge

Your Task: Create a calculator program that:

1. Asks the user for two numbers (they will be strings from input())
2. Converts them to floats
3. Calculates the sum, difference, product, and quotient
4. Prints results using str() to combine text and numbers

Key Takeaways

• int() converts to whole numbers (removes decimals)
• float() converts to decimal numbers
• str() converts to text
• input() always returns a string - convert it if you need numbers
• Cannot add strings and numbers directly
• Not all conversions are possible - check your data first

Great Progress! Next: String Operations - Working with Text