Python float() Function

The float() function in Python is used to convert a number or a string into a floating-point number (i.e., a decimal number).

This is helpful when you need precision or decimal values in your calculations.

Syntax

float([value])

Parameters:

• value (optional) – A number or a string that looks like a number.

Returns:

• A floating-point number (decimal).

Example 1: Convert Integer to Float

x = float(5)
print(x)

5.0

Example 2: Convert String to Float

price = float("19.99")
print(price)

19.99

Example 3: Using float() Without Any Argument

x = float()
print(x)

0.0

If no value is given, float() returns 0.0.

Example 4: Convert Scientific Notation String

num = float("1e3")
print(num)

1000.0

Use Case: Why Use float()?

• When reading decimal values from user input
• For precise calculations (e.g., percentages, interest rates)
• To convert values before arithmetic operations

Common Mistakes

• Passing a non-numeric string:

float("hello")  # ❌ Raises ValueError

• Expecting exact decimal representations: due to floating-point precision, results like 0.1 + 0.2 may not be exactly 0.3.

Interview Tip

In coding interviews, float() is often used for type conversion before performing arithmetic or formatting results.

Summary

• float() converts int, str, or no argument to a decimal number
• Raises ValueError for invalid strings
• Returns 0.0 if called with no arguments

Practice Problem

Ask the user for a price and discount percentage, then calculate and print the final price.

price = float(input("Enter the price: "))
discount = float(input("Enter the discount %: "))
final_price = price - (price * discount / 100)
print("Final price after discount:", final_price)