_alphanum_str = set('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890')
_alphanum_bytes = set(b'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890')

def escape(pattern):
    "Escape all non-alphanumeric characters in pattern."
    if isinstance(pattern, str):
        alphanum = _alphanum_str
        s = list(pattern)
        for i in range(len(pattern)):
            c = pattern[i]
            if c not in alphanum:
                if c == '\000':
                    s[i] = '\\000'
                else:
                    s[i] = '\\' + c
        return ''.join(s)
    else:
        alphanum = _alphanum_bytes
        s = []
        esc = ord(b'\\')
        for c in pattern:
            if c in alphanum:
                s.append(c)
            else:
                if c == 0:
                    s.extend(b'\\000')
                else:
                    s.append(esc)
                    s.append(c)
        return bytes(s)