schema.py 文件源码

def _to_index(index, table=None, engine=None):
    """Return if instance of Index, else construct new with metadata"""
    if isinstance(index, sqlalchemy.Index):
        return index

    # Given: index name; table name required
    table = _to_table(table, engine)
    ret = sqlalchemy.Index(index)
    ret.table = table
    return ret



# Python3: if we just use:
#
#     class ColumnDelta(DictMixin, sqlalchemy.schema.SchemaItem):
#         ...
#
# We get the following error:
# TypeError: metaclass conflict: the metaclass of a derived class must be a
# (non-strict) subclass of the metaclasses of all its bases.
#
# The complete inheritance/metaclass relationship list of ColumnDelta can be
# summarized by this following dot file:
#
# digraph test123 {
#     ColumnDelta -> MutableMapping;
#     MutableMapping -> Mapping;
#     Mapping -> {Sized Iterable Container};
#     {Sized Iterable Container} -> ABCMeta[style=dashed];
#
#     ColumnDelta -> SchemaItem;
#     SchemaItem -> {SchemaEventTarget Visitable};
#     SchemaEventTarget -> object;
#     Visitable -> {VisitableType object} [style=dashed];
#     VisitableType -> type;
# }
#
# We need to use a metaclass that inherits from all the metaclasses of
# DictMixin and sqlalchemy.schema.SchemaItem. Let's call it "MyMeta".