Import error on django models.py

Question

I wrote this funcion on a utils.py located on the app direcroty:

from bm.bmApp.models import Client

def get_client(user):
    try:
        client = Client.objects.get(username=user.username)
    except Client.DoesNotExist:
        print "User Does not Exist"
        return None
    else:       
        return client

def to_safe_uppercase(string):
    if string is None:
        return ''
    return string.upper()

Then when i use the function to_safe_uppercase on my models.py file, by importing it in this way:

from bm.bmApp.utils import to_safe_uppercase

I got the python error:

     from bm.bmApp.utils import to_safe_uppercase
ImportError: cannot import name to_safe_uppercase

I got the solution for this problem when i change the import statement for:

from bm.bmApp.utils import *

But i can't understand why is this, why when i import the specific function i got the error?

This should not happen. I suspect there is something else going on. — Marcin
– Marcin, Commented Apr 18, 2012 at 15:41
unfortunately, django by default catches ImportErrors and replaces them with this errormessage. try to patch django, so that it gives you the traceback, this should point to the problem. I suspect cyclic imports or something like that. — ch3ka
– ch3ka, Commented Apr 18, 2012 at 15:46
@ch3ka patching django isn't a great idea... also he is getting the python traceback already. He's pasted part of it in the question — Jiaaro
– Jiaaro, Commented Apr 18, 2012 at 15:48
@Jiaaro not for production use, of course. And I don't think that's the full traceback, as said, django used to hide it (not sure it that's true for recent versions, though) But Mark spotted the Problem already anyways: as I suspected, it's a circular import. — ch3ka
– ch3ka, Commented Apr 18, 2012 at 15:50

Jiaaro · Accepted Answer · 2012-04-18 15:54:53Z

You are doing what is known as a Circular import.

models.py:

from bm.bmApp.utils import to_safe_uppercase

utils.py:

from bm.bmApp.models import Client

Now when you do import bm.bmApp.models The interpreter does the following:

models.py - Line 1: try to import bm.bmApp.utils
utils.py - Line 1: try to import bm.bmApp.models
models.py - Line 1: try to import bm.bmApp.utils
utils.py - Line 1: try to import bm.bmApp.models
...

The easiest solution is to move the import inside the function:

utils.py:

def get_client(user):
    from bm.bmApp.models import Client
    try:
        client = Client.objects.get(username=user.username)
    except Client.DoesNotExist:
        print "User Does not Exist"
        return None
    else:       
        return client

def to_safe_uppercase(string):
    if string is None:
        return ''
    return string.upper()

Mark Lavin · Accepted Answer · 2012-04-18 15:46:30Z

8

You are creating a circular import.

utils.py
from bm.bmApp.models import Client
# Rest of the file...

models.py
from bm.bmApp.utils import to_safe_uppercase
# Rest of the file...

I would suggest your refactor your code so that you don't have a circular dependency (i.e. utils should not need to import models.py or vice versa).

answered Apr 18, 2012 at 15:46

Mark Lavin

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3 Comments

Mark Lavin Over a year ago

See docs.python.org/faq/…

jadkik94 Over a year ago

Thanks. You should consider adding something about it in your answer, it's part of the OP's question. :)

alacret Over a year ago

I've checking the link above, and it seems this get this problem:

BenMorel · Accepted Answer · 2014-01-08 11:35:18Z

0

I'm not sure I can explain the Import error, but I have three ideas. First, your function needs tweaking. You've used a reserved word 'string' as an argument. Consider renaming.

Second, what happens if you invoke ./manage.py shell, and do the import by hand. Does it give you any different?

Third, try deleting your pyc files to force django to recompile python code (this one is a very long shot...but worth eliminating)

edited Jan 8, 2014 at 11:35

BenMorel

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answered Apr 18, 2012 at 15:44

user590028

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