Reversing Python's re.escape

So is this really the only thing that works?

>>> re.sub(r'\\(.)', r'\1', re.escape(' '))
' '

Yes. The source for the re module contains no unescape() function, so you're definitely going to have to write one yourself.

Furthermore, the re.escape() function uses str.translate() …

def escape(pattern):
    """
    Escape special characters in a string.
    """
    if isinstance(pattern, str):
        return pattern.translate(_special_chars_map)
    else:
        pattern = str(pattern, 'latin1')
        return pattern.translate(_special_chars_map).encode('latin1')

… which, while it can transform a single character into multiple characters (e.g. [ → \[), cannot perform the reverse of that operation.

Since there's no direct reversal of escape() available via str.translate(), a custom unescape() function using re.sub(), as described in your question, is the most straightforward solution.