Python Basics: How Do You Correctly Convert a String Like “3.9” to an Integer in Python?

Why Does Python’s int() Function Raise a ValueError for Strings with Decimals?

Discover why executing int(“3.9”) in Python results in a ValueError. The int() function requires a string to be a valid integer literal, and the decimal point violates this rule. Learn the correct way to convert a string containing a decimal point to an integer.

Question

What happens when you execute int(“3.9”)?

A. It returns “3” as a string
B. It raises a ValueError
C. It returns 4 due to rounding
D. It returns 3

Answer

B. It raises a ValueError

Explanation

The string contains a decimal point and is not a valid integer literal.

The built-in int() function can convert a string to an integer, but only if the string contains a valid integer literal. A valid integer literal consists only of digits and an optional leading sign (+ or -).

The string “3.9” contains a decimal point (.), which means it represents a floating-point number, not an integer. The int() function’s parser cannot process the decimal point and therefore raises a ValueError with a message like invalid literal for int() with base 10: ‘3.9’.

To successfully convert a numeric string with a decimal into an integer, you must first convert it to a float, which truncates (not rounds) the decimal part.

# This is the correct two-step process
float_value = float("3.9") # Returns 3.9
integer_value = int(float_value) # Returns 3

This explains why the other options are incorrect:

• The function never returns a string; its purpose is to return an integer.
• It does not round, so it would not return 4.
• It cannot directly truncate the string to return 3 because the ValueError occurs before any conversion can happen.

Python Basics: Learn, Apply & Build Programs certification exam assessment practice question and answer (Q&A) dump including multiple choice questions (MCQ) and objective type questions, with detail explanation and reference available free, helpful to pass the Python Basics: Learn, Apply & Build Programs exam and earn Python Basics: Learn, Apply & Build Programs certificate.