For internal, see _remove_buffers

def _separate_buffers(substate, path, buffer_paths, buffers):
    """For internal, see _remove_buffers"""
    # remove binary types from dicts and lists, but keep track of their paths
    # any part of the dict/list that needs modification will be cloned, so the original stays untouched
    # e.g. {'x': {'ar': ar}, 'y': [ar2, ar3]}, where ar/ar2/ar3 are binary types
    # will result in {'x': {}, 'y': [None, None]}, [ar, ar2, ar3], [['x', 'ar'], ['y', 0], ['y', 1]]
    # instead of removing elements from the list, this will make replacing the buffers on the js side much easier
    if isinstance(substate, (list, tuple)):
        is_cloned = False
        for i, v in enumerate(substate):
            if isinstance(v, _binary_types):
                if not is_cloned:
                    substate = list(substate) # shallow clone list/tuple
                    is_cloned = True
                substate[i] = None
                buffers.append(v)
                buffer_paths.append(path + [i])
            elif isinstance(v, (dict, list, tuple)):
                vnew = _separate_buffers(v, path + [i], buffer_paths, buffers)
                if v is not vnew: # only assign when value changed
                    if not is_cloned:
                        substate = list(substate) # clone list/tuple
                        is_cloned = True
                    substate[i] = vnew
    elif isinstance(substate, dict):
        is_cloned = False
        for k, v in substate.items():
            if isinstance(v, _binary_types):
                if not is_cloned:
                    substate = dict(substate) # shallow clone dict
                    is_cloned = True
                del substate[k]
                buffers.append(v)
                buffer_paths.append(path + [k])
            elif isinstance(v, (dict, list, tuple)):
                vnew = _separate_buffers(v, path + [k], buffer_paths, buffers)
                if v is not vnew: # only assign when value changed
                    if not is_cloned:
                        substate = dict(substate) # clone list/tuple
                        is_cloned = True
                    substate[k] = vnew
    else:
        raise ValueError("expected state to be a list or dict, not %r" % substate)
    return substate