optional import of subpackages

[svenkreiss]

Steps to reproduce

Pylint is happy but scipy.ndimage is not imported:

try:
    import scipy
except ImportError:
    scipy = None

Need the import below to make scipy.ndimage available, but pylint complains:

try:
    import scipy.ndimage  # <--- need to import ndimage like this otherwise not imported
except ImportError:
    scipy = None

Pylint: C0103: Constant name "scipy" doesn't conform to UPPER_CASE naming style (invalid-name)

Expected behavior (updated)

When I run pylint, I want the output to be:

Context

I am making scipy an optional dependency in OpenPifPaf: openpifpaf/openpifpaf#390

[dbaty]

In the second form, you define two different symbols: scipy.ndimage if scipy is installed; scipy otherwise. How do you cope with this discrepancy in the rest of the module?

I would suggest doing something like this:

try:
    import scipy.ndimage as scipy_ndimage
except ImportError:
    scipy_ndimage = None

def foo():
    if scipy_ndimage:
         return scipy_ndimage.frobulate()
    return 2  # good approximation of the frobulation algorithm without scipy

Alternatively:

try:
    import scipy
    import scipy.ndimage
except ImportError:
    scipy = None

def foo():
    if scipy:
         return scipy.ndimage.frobulate()
    return 2  # good approximation of the frobulation algorithm without scipy

(It's untested and I hope it's not too far from something that would work!)

[hippo91]

@svenkreiss thanks for you report.
@dbaty thanks for your research and explanation.
@svenkreiss are you ok with @dbaty's advice?
If so i will close the issue.

[svenkreiss]

@dbaty I didn't follow your two different symbols argument. When I import scipy.ndimage then that is not just one thing. After the import, I do have access to scipy as well:

I'd argue that my original code is valid and should not fail pylint.

[Pierre-Sassoulas]

I don't understand this issue, what would you want pylint to do exactly ? Not raise a C0103: Constant name "scipy" doesn't conform to UPPER_CASE naming style on scipy = None ? There is an issue template for a reason.

[svenkreiss]

Yes, I don't want pylint to raise this C0103.

I have updated the report with the relevant part from the issue template (apologies @Pierre-Sassoulas ).

[Pierre-Sassoulas]

Thank you for the clarification @svenkreiss, I'm going to close as duplicate of #3585 .