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Complete this python program:
def convert_to_symbolic_indices(seq, start=None, gen=None, qubit_map=None):
assistant
#Here is the Python code you requested.

    """Returns the circuit with symbolic indices and the
    dictionary mapping symbolic indices to real indices.
    The mapping is 1 to 1 and onto (bijective).
    Parameters
    seq : tuple, Gate/Integer/tuple or Mul
    A tuple of Gate, Integer, or tuple objects, or a Mul
    start : Symbol
    An optional starting symbolic index
    gen : object
    An optional numbered symbol generator
    qubit_map : dict
    An existing mapping of symbolic indices to real indices
    All symbolic indices have the format \i#\, where # is
    some number >= 0.
    """
    if isinstance(seq, Mul):
        seq = seq.args
    index_gen = numbered_symbols(prefix='i', start=(-1))
    cur_ndx = next(index_gen)
    ndx_map = {}
    def create_inverse_map(symb_to_real_map):
        rev_items = (lambda item: tuple([item[1], item[0]]))
        return dict(map(rev_items, symb_to_real_map.items()))
    if (start is not None):
        if (not isinstance(start, Symbol)):
            msg = ('Expected    Symbol    for    starting    index,    got    %r.' % start)
            raise TypeError(msg)
        cur_ndx = start
    if (gen is not None):
        if (not isinstance(gen, numbered_symbols().__class__)):
            msg = ('Expected    a    generator,    got    %r.' % gen)
            raise TypeError(msg)
        index_gen = gen
    if (qubit_map is not None):
        if (not isinstance(qubit_map, dict)):
            msg = ('Expected    dict    for    existing    map,    got    ' + ('%r.' % qubit_map))
            raise TypeError(msg)
        ndx_map = qubit_map
    ndx_map = _sympify_qubit_map(ndx_map)
    inv_map = create_inverse_map(ndx_map)
    sym_seq = ()
    for item in seq:
        if isinstance(item, Gate):
            result = convert_to_symbolic_indices(item.args, qubit_map=ndx_map, start=cur_ndx, gen=index_gen)
            (sym_item, new_map, cur_ndx, index_gen) = result
            ndx_map.update(new_map)
            inv_map = create_inverse_map(ndx_map)
        elif (isinstance(item, tuple) or isinstance(item, Tuple)):
            result = convert_to_symbolic_indices(item, qubit_map=ndx_map, start=cur_ndx, gen=index_gen)
            (sym_item, new_map, cur_ndx, index_gen) = result
            ndx_map.update(new_map)
            inv_map = create_inverse_map(ndx_map)
        elif (item in inv_map):
            sym_item = inv_map[item]
        else:
            cur_ndx = next(gen)
            ndx_map[cur_ndx] = item
            inv_map[item] = cur_ndx
            sym_item = cur_ndx
        if isinstance(item, Gate):
            sym_item = item.__class__(*sym_item)
       ...