If validate=True is passed to base64.b64decode(), it should raise a binascii.Error if the input contains any character not from the acceptable alphabet.

But it does not raise if the input ends with a single \n. It raises if the input ends with a multiple \n or with any other whitespace character. Only a single \n is accepted.

This is an implementation artifact. A regular exception ending with $ is used to validate an input. But $ matches not only end of string. It matches also an empty string before the trailing \n.

Similar errors are also occurred in other sites. I'll open separate issues for different cases.