Silent importing of submodules differs from standard Python3.2 interpreter's behavior

[brannerchinese]

I have a question about Ipython3: importing modules that contain submodules. If I import urllib as U, I can then call U.request.urlopen() and Ipython3 correctly loads the method in question.

But if I use the same commands in the regular python3.2 interpreter, I get an error: "AttributeError: 'module' object has no attribute 'request' ".

It seems Ipython3 is loading submodules, unbidden, while python3.2 does not; that means that code may work on Ipython3 but not at the command line. Is this intentional? Is it documented? I do not see it in the docs, however.

(Environment: Python v. 3.2.3/Ipython 0.13.1 on Ubuntu 12.04 and OS 10.8)

[minrk]

I think it's just that IPython had already imported urllib.request for its own use before you did.

To check:

In [1]: import sys; print('urllib.request' in sys.modules)
True

and to further check your suspicions for modules in general with a dummy package:

mkdir mymod
touch mymod/__init__.py
echo "foo=5" > mymod/submod.py
ipython

In [1]: import mymod
In [2]: mymod.<TAB>
<no results>
In [3]: import mymod.submod
In [4]: mymod.<TAB>
In [4]: mymod.submod

So I don't think anything untoward is going on.

[brannerchinese]

Thanks, minrk, for your quick reply.

The only untoward thing is that after the user tests code on Ipython, the same code must be tested on the regular interpreter or command line, lest necessary modules not have been imported correctly. I wonder if there is a way to make this extra step unnecessary.

[minrk]

I don't think there is anything to do, other than minimize the things IPython imports itself. The fact that one package's imports can affect how modules look to other code in the same process is just an artefact of how Python works.

[takluyver]

In this specific case, I think it should be fixed by #2868, which defers importing urllib until a method is called that needs it.

[brannerchinese]

All true, but the fact is that urllib is being treated as a special case for use in Ipython. I can't really see the value of this, as it requires the user to do extra work to enable to same code to run correctly in the standard interpreter.

[takluyver]

Just checked, this is fixed in master:

In [1]: import urllib as U

In [2]: U.request.urlopen
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-2-cbeb1d4246db> in <module>()
----> 1 U.request.urlopen

AttributeError: 'module' object has no attribute 'request'

Do you see the issue with any other packages?

[brannerchinese]

Haven't noticed it elsewhere, but thank you!

[bfroehle]

I agree there isn't much else we can do here. Python doesn't really allow modules to be imported multiple times, so this is (as @minrk pointed out) an artifact of the way IPython and your script share the same Python interpreter.

Shall we close this issue?