def is_common(schema):
if isinstance(schema, StreamSchema):<EOL><INDENT>return schema.schema() in _SCHEMA_COMMON<EOL><DEDENT>if isinstance(schema, CommonSchema):<EOL><INDENT>return True<EOL><DEDENT>if isinstance(schema, basestring):<EOL><INDENT>return is_common(StreamSchema(schema))<EOL><DEDENT>return False<EOL>
Is `schema` an common schema.

Args:
    schema: Scheme to test.

Returns:
    bool: ``True`` if schema is a common schema, otherwise ``False``.