Undoes the effects of the escape() function.

def unescape(str):
    """Undoes the effects of the escape() function."""
    out = ''
    prev_backslash = False
    for char in str:
        if not prev_backslash and char == '\\':
            prev_backslash = True
            continue
        out += char
        prev_backslash = False
    return out