> If untabify fails because a file has an incorrect encoding, is it really
> a problem in untabify? This is a developer’s tool, so getting a
> traceback here seems okay to me.

I disagree.  I think we should use this opportunity to clarify preferred encoding for C language source files in python and make untabify produce meaningful diagnostic in case of encoding errors.

As a matter of policy, I see two possibilities:

1. Restrict C sources to 7-bit ASCII.  (A pedantic reading of ANSI C standard would probably suggest even more restricted character set, but practically, I don't think 7-bit ASCII in C comments is likely to cause problems for any tools.

2. Require UTF-8 encoding for non-ASCII characters.  Given that this is the default for python source code, it is likely that tools that are used for python development can handle UTF-8.

My vote is for #1.  Display of non-ascii characters is still not universally supported and they are likely to be clobbered when diffs are copied in e-mails etc.