fix an error message of confusion_matrix.IoU

[junbao-zhou]

Description:

An error message in ignite.metrics.confusion_matrix.IoU is confusing and does not match the condition check, which might lead to misunderstanding. I update the error message to make it match the condition check.

Check list:

• New tests are added (if a new feature is added)
• New doc strings: description and/or example code are in RST format
• Documentation is updated (if required)

[vfdev-5]

@BowmanChow thanks for the PR, I let @sadra-barikbin review it and comment out

[sadra-barikbin]

Hi @BowmanChow , thanks for the PR. Could you please apply this change to other places of confusion_matrix.py? For example line 396.

[junbao-zhou]

Hi @sadra-barikbin , I made another change and force-pushed, because I want to keep the commit tree clean. I'm not sure whether force-push is ok. Is it mergable?

[vfdev-5]

@BowmanChow yes, it is ok to push-force. As it is your first contribution we need to approve to run the CI.

By the way, can you please check if there is a confusion matrix test which check for previous message error. If there is one, then it will fail now as you changed the error message.

Please fix:

+ flake8 ignite tests examples --config setup.cfg
ignite/metrics/confusion_matrix.py:242:121: E501 line too long (131 > 120 characters)
ignite/metrics/confusion_matrix.py:396:121: E501 line too long (131 > 120 characters)

[junbao-zhou]

@vfdev-5 I'm sorry that I thought my changes were so small and don't need a check. I will have the formatting and test run.

[junbao-zhou]

Hi @vfdev-5 , I've completed the formatting and test_confusion_matrix.py check.

[vfdev-5]

Thanks for the PR @BowmanChow ! LGTM
CI failures are unrelated. I'll merge your PR once we fixed issues on master and I updated your PR.