python - Metaclass conflict when separating classes into separate files -


edit

the problem in importing. should have done write: from someinterface import someinterface. should write module name in lowercase someinterface.py per python styleguide (pep 8).

i have file model.py defines classes related db instantiates base. 

# model.py metadata = metadata() declarativebase = declarative_base() metadata = declarativebase.metadata  class bar(declarativebase):     __tablename__ = 'bar'     __table_args__ = {}     # column , relation definitions

the file model.py autogenerated can't touch it. did instead create file called modelaugmented.py add functionality of model classes via inheritance.

# modelaugmented.py model import * import someinterface  class baraugmented(bar, someinterface):     pass  # someinterface.py class someinterface(object):     some_method(): pass

the problem i'm having classes baraugmented, i'm getting following error: 

 typeerror: error when calling metaclass bases  metaclass conflict: metaclass of derived class must (non-strict) subclass of metaclasses of bases

i error when someinterface in separate file instead of being inside modelaugmented.py.

i understand metaclass someinterface , bar different. problem can't figure out how resolve problem. tried solution suggested in triple inheritance causes metaclass conflict... sometimes works in example given, not in case. not sure if sqlalchmey has it.

class metaab(type(declarativebase), type(someinterface)):     pass  class baraugmented(bar, someinterface):     __metaclass__ = metaab

but error:

typeerror: error when calling metaclass  bases multiple bases have instance lay-out conflict

using sqlalchemy 0.8 , python 2.7.

ok, there must i'm missing, because created similar file layout yours (i think) , works in machine. appreciate kept question short , simple, maybe missing little detail alters... something? dunno... (maybe someinterface has abc.abstract metaclass?) if update question, please let me know trough comment answer, , i'll try update answer.

here goes:

file stack29a.py (equivalent model.py):

from sqlalchemy import create_engine, column, integer, string sqlalchemy.ext.declarative import declarative_base sqlalchemy.orm import sessionmaker, scoped_session  dsn = "mysql://root:foobar@localhost/so_tests?charset=utf8" engine = create_engine(dsn) session = scoped_session(sessionmaker(bind=engine)) session = session()  declarativebase = declarative_base()  class bar(declarativebase):     __tablename__ = 'bar'     _id = column('_id', integer, primary_key=true)     email = column('email', string(50))

file stack29b.py (equivalent someinterface.py):

class someinterface(object):     def some_method(self):         print "hellou"

file stack29c.py (equivalent modelaugmented.py):

from stack29a import bar stack29b import someinterface  class baraugmented(bar, someinterface):     pass

file stack29d.py (like kind of main.py: table creator , sample):

from stack29c import baraugmented stack29a import session, engine, declarativebase  if __name__ == "__main__":     declarativebase.metadata.create_all(engine)     b1 = baraugmented()     b1.email = "foo@bar.baz"     b2 = baraugmented()     b2.email = "baz@bar.foo"     session.add_all([b1, b2])     session.commit()     b3 = session.query(baraugmented)\                     .filter(baraugmented.email == "foo@bar.baz")\                     .first()     print "b3.email: %s" % b3.email                         b3.some_method()

if run "main" file (stack29d.py) works expected:

(venv_so)borrajax@borrajax:~/documents/tests$ python ./stack29d.py b3.email: foo@bar.baz hellou

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