Python conditional 'module object has no attribute' error with personal package distinct from circular import issue

Question

I'm getting a 'module object has no attribute ..." error when trying to use a package heirarchy I created. The error is reminiscant of the error you get when there is a circular import (i.e. module a imports b and module b imports a), but I can't see that issue here. I've gone through many posts with a similar error, but none of the explanations I saw quite fit.

This was seen with python 2.7.1 and python 2.4.3.

I've watered it down to the following example:

Consider the following heirarchy (see code below):

alpha
alpha/__init__.py
alpha/bravo
alpha/bravo/__init__.py
alpha/bravo/charlie.py
alpha/bravo/delta.py
alpha/bravo/echo.py

The module charlie imports echo which in turn imports delta. If the alpha/bravo/__init__.py (like alpha/__init__.py) is essentially blank, a script can do:

import alpha.bravo.charlie

The problem surfaces if I try to import alpha.bravo.charlie in alpha/bravo/__init__.py (with the thinking I could surface relevant classes/methods there, and a script would do 'import alpha.bravo').

Code:

alpha/__init__.py

(blank)

alpha/bravo/__init__.py

import alpha.bravo.charlie

alpha/bravo/charlie.py

import alpha.bravo.echo
def charlie_foo(x): return str(x)
def charlie_bar(x): return alpha.bravo.echo.echo_biz()

alpha/bravo/delta.py

def delta_foo(x): return str(x)

alpha/bravo/echo.py

import alpha.bravo.delta
print alpha.bravo.delta.delta_foo(1)
def echo_biz(): return 'blah'

If I try:

python -c 'import alpha.bravo'

I get:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/kmkc980/svn/working/azcif/python/lib/alpha/bravo/__init__.py", line 1, in <module>
    import alpha.bravo.charlie
  File "/home/kmkc980/svn/working/azcif/python/lib/alpha/bravo/charlie.py", line 1, in <module>
    import alpha.bravo.echo
  File "/home/kmkc980/svn/working/azcif/python/lib/alpha/bravo/echo.py", line 2, in <module>
    print alpha.bravo.delta.delta_foo(1)
AttributeError: 'module' object has no attribute 'bravo'

But, if I comment out the import line in alpha/bravo/__init__.py, then all seems OK:

python -c 'import alpha.bravo'

python -c 'import alpha.bravo.charlie'
1

Moreover, if I use the same code above (including the import line in alpha/bravo/__init__.py), but edit everything to exclude the 'alpha' level of the hierarchy, it seems to work fine.

So the hierarchy is now just:

bravo
bravo/__init__.py
bravo/charlie.py
bravo/delta.py
bravo/echo.py

and I change all the lines with "alpha.bravo.*" to "bravo.*"

Then no problem:

python -c 'import bravo'
1

I've been able to work around the issue, but I'd still like to understand it. Thanks.

Answer 1

Instead of using absolute imports, it might help to use relatives.

i.e.

alpha/bravo/_init_.py

import alpha.bravo.charlie

should be

import charlie

Otherwise, it probably is a circular import. i.e. if you import alpha.bravo.charlie from charlie, that means

alpha/__init__.py
bravo/__init__.py
charlie/__init__.py 

All are loaded (or rather, prevented from doing so since they're already loaded). That might cause the problem you're seeing.