human
I wrote the below code

    def marker_var(remaining):
        m = IDENTIFIER.match(remaining)
        if m:
            result = m.groups()[0]
            remaining = remaining[m.end():]
        elif (not remaining):
            raise SyntaxError('unexpected    end    of    input')
        else:
            q = remaining[0]
            if (q not in '\'"'):
                raise SyntaxError(('invalid    expression:    %s' % remaining))
            oq = '\'"'.replace(q, '')
            remaining = remaining[1:]
            parts = [q]
            while remaining:
                if (remaining[0] == q):
                    break
                elif (remaining[0] == oq):
                    parts.append(oq)
                    remaining = remaining[1:]
                else:
                    m = STRING_CHUNK.match(remaining)
                    if (not m):
                        raise SyntaxError(('error    in    string    literal:    %s' % remaining))
                    parts.append(m.groups()[0])
                    remaining = remaining[m.end():]
            else:
                s = ''.join(parts)
                raise SyntaxError(('unterminated    string:    %s' % s))
            parts.append(q)
            result = ''.join(parts)
            remaining = remaining[1:].lstrip()
        return (result, remaining)
    def marker_expr(remaining):
        if (remaining and (remaining[0] == '(')):
            (result, remaining) = marker(remaining[1:].lstrip())
            if (remaining[0] != ')'):
                raise SyntaxError(('unterminated    parenthesis:    %s' % remaining))
            remaining = remaining[1:].lstrip()
        else:
            (lhs, remaining) = marker_var(remaining)
            while remaining:
                m = MARKER_OP.match(remaining)
                if (not m):
                    break
                op = m.groups()[0]
                remaining = remaining[m.end():]
                (rhs, remaining) = marker_var(remaining)
                lhs = {'op': op, 'lhs': lhs, 'rhs': rhs}
           ...

What's a good function header?

=====
Here's a good function header?
assistant
#Here's a good function header.

def parse_marker(marker_string):