Decoding Base64 Data with Padding Errors

Decoding base64 data is a common task in programming, but incorrect padding can hinder the process. While base64.decodestring raises an error upon encountering these padding errors, alternative methods are available.

One solution is to manually add the maximum number of padding characters, which is two. Python 3.x's base64.b64decode will automatically truncate any unnecessary characters.

This approach is simple and effective:

base64.b64decode(s   b'==')

Alternatively, use base64.b64decode(s b'=' * (-len(s) % 4)) to calculate the number of padding characters needed based on the length of the input.

If the input string already has padding, ensure that the validate keyword argument is set to False (default) to avoid an error.

If validate is set to False, you can blindly add two padding characters without issue. However, if validate is True, any non-alphabet characters in the input will cause an error.