How to debug Python import failure

Question

I have a directory structure:

network/__init__.py
network/model.py
network/transformer/__init__.py
network/transformer/t_model.py

both __init__.py files have appropriate

__all__ = [
    "model",  # or "t_model" in the case of transformer
    "view",
    ]

In t_model.py, I have

from .. import model

but it says:

ImportError: cannot import name model

If I try

from ..model import Node

it says:

ImportError: cannot import name Node

These are very confusing errors.

---

Edit: Even an absolute import fails:

import network as N
print(dir(N), N.__all__)
import network.model as M

['__all__', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__', 'transformer'] ['model', 'view']
Traceback (most recent call last):..........
AttributeError: 'module' object has no attribute 'model'

---

Edit: It was a circular import.

Solution

This works for me. Can you run/import model.py? If it has syntax errors you can't import it. (In general I recommend not to do relative imports, the use of them is limited).

Your absolute import is very confusing. The way to do an absolute import in this package is:

from network model import Node

This works fine.

I have a program.py in the top level (above network):

from network.transformer import t_model

And the t_model.py looks like this:

from .. import model
print "Model", model

from ..model import Node
print "Node", Node

from network.model import Node
print "Absolute", Node

And the output is:

Model <module 'network.model' from '/tmp/network/model.pyc'>
Node <class 'network.model.Node'>
Absolute <class 'network.model.Node'>

So as you can see it works fine your error is somewhere else.

Comments

[Neil G]

Thanks. I have __init__.py in every folder.

[Neil G]

If I do from network.model import Node, it says ImportError: cannot import name Node

[Lennart Regebro]

@Neil G: Of course. As I showed above above your relative imports are correct, the error is somewhere else, not in how you write the import. Now if you read my answer, you'll see that I ask you a question. If you want help with this I suggest you answer it.

[Neil G]

Importing model.py was the problem. It turned out that model.py was importing t_model.py, which imported model.py. I was almost pulling my hair out on this one. Thank you very much for your help.

[Neil G]

Also, is it true that I should prefer absolute imports to relative ones? Or vice versa?

[Lennart Regebro]

@Neil G: Super! Glad to help! In my experience you almost never need relative imports, and absolute imports cause less confusion. :-)