How do you deal with multiple Python classes in the same module depending on each other?

Question

I'm using an ODM library and I'm defining documents as classes within the same module, when they are related. I've hit a circular dependency problem and because I haven't come across this before in Python, I don't know how to inform the classes of the existence of each other. Example:

''' docs.py '''
from mongoengine import Document
from mongoengine.fields import StringField, ReferenceField, ListField


class Base(Document):
    some_field      = StringField()


class Foo(Base):
    other_field     = StringField()
    another_field   = ReferenceField(Bar)


class Bar(Base):
    other_field     = StringField()
    another_field   = ListField(ReferenceField(Foo))

As it stands the Python will throw a NameError because Bar is not defined when the interpreter gets to a reference to it in the file, within the class Foo. How do I tell Python not to worry and that the class definition will be along shortly?

possible duplicate of [Python mutually dependent classes (circular dependencies)](http://stackoverflow.com/questions/6402522/python-mutually-dependent-classes-circular-dependencies) — Shawn Chin, Dec 01 '11 at 11:45
@ShawnChin: I don't think the solution in the linked question applies here, so it's not a real duplicate. — Sven Marnach, Dec 01 '11 at 11:58

score 5 · Accepted Answer · answered Dec 01 '11 at 11:45

5

ReferenceField accepts class name as well.

another_field   = ReferenceField('Bar')

answered Dec 01 '11 at 11:45

DrTyrsa

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I didn't know that (doesn't mention it in the API docs), the approach of referencing `A.field = ReferenceField(B)` is probably more applicable to Python generally, but I think this approach is preferable here because it maintains readability in the module (all document fields grouped together) – Edwardr 9 secs ago edit – Edwardr Dec 01 '11 at 12:03

How do you deal with multiple Python classes in the same module depending on each other?

1 Answers1