encode short string as filename (unix/windows)

[nikie]

> want to encode/decode an arbitrary short 8-bit string as save filename.
> is there a good already builtin encoding to do this (without too much
> inflation) ? or re.sub expression?
>
> or which characters are not allowed in filenames on typical OS?

On Windows, / \ : * ?  " < > | are forbidden, and the name can't be
empty.

Using urlsafe_b64encode/...decode should work on any platform.