scipy.signal doesn't allow for user modules to be named `constants`

If you have a module named constants in your project, then if you try to use that module while at the same time using scipy.signal (and it seems any module that uses scipy.optimize), you’ll get an exception. It seems to be related to https://github.com/scipy/scipy/blame/master/scipy/optimize/_highs/cython/src/constants.pyx

Reproducing code example:

#!/bin/sh

# Don't run this in a place where you have an existing file named `constants.py`
echo "MY_IMPORTANT_CONSTANT = 1" > constants.py
python3 -c "from scipy import signal; import constants; print(constants.MY_IMPORTANT_CONSTANT)"
rm constants.py

Error message:

Traceback (most recent call last):
  File "<string>", line 3, in <module>
AttributeError: module 'scipy.optimize._highs.constants' has no attribute 'MY_IMPORTANT_CONSTANT'

Scipy/Numpy/Python version information:

1.6.0 1.19.4 sys.version_info(major=3, minor=9, micro=1, releaselevel='final', serial=0)

[153957]

We encountered the same issue. We resolved it by renaming our constants module to something else (which was fine, we did not like the name anyway), but it is an annoying bug.

[mikemikezhu]

Also encountered same issue when importing the constants module

ImportError: cannot import name 'IMAGE_NET_DISPLAY_ROW' from 'scipy.optimize._highs.constants'

Need to work around the issue by renaming the constants module in the project