'Guess the extension for a file based on its MIME type.
Return value is a string giving a filename extension,
including the leading dot (\'.\').  The extension is not
guaranteed to have been associated with any particular data
stream, but would be mapped to the MIME type `type\' by
guess_type().  If no extension can be guessed for `type\', None
is returned.
Optional `strict\' argument when false adds a bunch of commonly found,
but non-standard types.'

def guess_extension(self, type, strict=True):

    extensions = self.guess_all_extensions(type, strict)
    if (not extensions):
        return None
    return extensions[0]
