Is ValueError an appropriate exception to raise if user passes arguments of different lengths, which meant to be the same?

Question

In a function, I want to make sure arguments a and b have the same length. I want to raise an Exception for this if not complied. I know ValueError is for exception where an argument itself doesn't conform some particular criteria. Is ValueError an appropriate error to raise in this case where criteria is between arguments? If not, any standard Python exception more appropriate?

def func(a, b):
    if len(a) != len(b):
        raise ValueError("list a and list b must have the same length")

you can simply return stating that the lists need to be the same length — Padraic Cunningham, Feb 14 '15 at 10:35
Yes, I would say `ValueError` is the appropriate choice; your current implementation is fine. — jonrsharpe, Feb 14 '15 at 10:37
And for those tempted to suggest using `assert` / `AssertionError`, please see http://stackoverflow.com/questions/944592/best-practice-for-python-assert — PM 2Ring, Feb 14 '15 at 11:29

nijoakim · Answer 1 · 2022-11-28T08:54:05.857

As johnrsharpe points out in the comments, ValueError is the appropriate choice.

Another contender would be IndexError, as suggested by Wikiii122. However, according to the Python docs,

exception IndexError

Raised when a sequence subscript is out of range. (Slice indices are silently truncated to fall in the allowed range; if an index is not a plain integer, TypeError is raised.)

This is likely what would be raised anyway if you didn't bother to raise an exception, but is not as descriptive as ValueError whose documention is as follows:

exception ValueError

Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception such as IndexError.

@rudolfbyker: Yes, you are right! I corrected it now. Thank you! — nijoakim, Apr 03 '18 at 11:51

Is ValueError an appropriate exception to raise if user passes arguments of different lengths, which meant to be the same?

1 Answers1