New submission from Xiang Zhang <[email protected]>:
While debugging a problem in my job I find an odd case about import, it could
be reduced to the following tracebacks:
>>> from keystone.assignment import schema
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/site-packages/keystone/assignment/__init__.py", line
15, in <module>
from keystone.assignment import controllers # noqa
File "/usr/lib/python2.7/site-packages/keystone/assignment/controllers.py",
line 26, in <module>
from keystone.common import controller
File "/usr/lib/python2.7/site-packages/keystone/common/controller.py", line
24, in <module>
from keystone.common import authorization
File "/usr/lib/python2.7/site-packages/keystone/common/authorization.py",
line 23, in <module>
from keystone.models import token_model
File "/usr/lib/python2.7/site-packages/keystone/models/token_model.py", line
15, in <module>
from keystoneclient.common import cms
ImportError: No module named keystoneclient.common
>>> from keystone.assignment import schema
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.7/site-packages/keystone/assignment/__init__.py", line
15, in <module>
from keystone.assignment import controllers # noqa
File "/usr/lib/python2.7/site-packages/keystone/assignment/controllers.py",
line 25, in <module>
from keystone.assignment import schema
ImportError: cannot import name schema
keystoneclient is deliberately not installed. I think it should always report
keystoneclient.common could not be found which reveals the root causes. But
only the first time it does so. Later tries it always report cannot import
schema.
The reason of this behaviour is that first time although keystone.assignment
import fails but keystone.assignment.schema is successfully installed in
sys.modules. And then, in ensure_fromlist, it calls import_submodule which
returns the module in sys.modules, without set schema attribute to
keystone.assignment. So it then fails in import_from for not able to get the
attribute.
It could be simply reproduced by the following package structure:
test
|-- a.py
|-- b.py
`-- __init__.py
__init__.py:
from test import a
a.py:
from test import b
import modulenotexisting
b.py: #emtpy
>>> import test
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "test/__init__.py", line 1, in <module>
from test import a
File "test/a.py", line 2, in <module>
import dddddddddd
ImportError: No module named dddddddddd
>>> import test
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "test/__init__.py", line 1, in <module>
from test import a
File "test/a.py", line 1, in <module>
from test import b
ImportError: cannot import name b
Python3 doesn't suffer this problem, at least for 3.7.
I don't know this should be identified as a bug or not. But this does bring me
trouble debugging problems and lead to confusions because it doesn't tell
users the real module can't be imported.
----------
components: Interpreter Core
messages: 309360
nosy: brett.cannon, eric.snow, ncoghlan, xiang.zhang
priority: normal
severity: normal
status: open
title: inconsistent ImportError message executing same import statement
type: behavior
versions: Python 2.7
_______________________________________
Python tracker <[email protected]>
<https://bugs.python.org/issue32479>
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