Table of Contents
How Do You Prevent String Concatenation When Adding Numbers from Python’s input()?
Learn why Python’s input() function returns a string and why you must convert it using float() or int() to perform correct numeric addition instead of string concatenation. Avoid common errors where “2” + “3” becomes “23” instead of 5.
Question
Why convert user input with float(input(…)) before performing addition?
A. To convert numbers to booleans
B. To speed up execution
C. To automatically round to the nearest integer
D. To ensure numeric addition instead of string concatenation
Answer
D. To ensure numeric addition instead of string concatenation
Explanation
Without conversion, “2” + “3” yields “23”, not 5.
Converting user input is necessary to ensure the + operator performs numeric addition instead of string concatenation.
In Python, the input() function always returns the user’s entry as a string, regardless of whether the user typed numbers or letters. The + operator behaves differently based on the data types it is given:
- When used with numbers (integers or floats), + performs mathematical addition. For example, 2.0 + 3.0 equals 5.0.
- When used with strings, + performs concatenation, which joins the strings together. For example, “2” + “3” results in the string “23”.
By wrapping the input() function with float(), you are explicitly converting the returned string (e.g., “3.14”) into a floating-point number (e.g., 3.14). This ensures that when you use the + operator, Python will perform the correct mathematical calculation.
The other options are incorrect:
A: The float() function converts a value to a floating-point number, not a boolean (True or False).
B: The conversion is a required step for correctness and does not inherently speed up the program.
C: The float() function preserves the decimal value. The int() function would truncate (not round) it, and neither function automatically rounds to the nearest integer.
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