Use raise .. from .. to explicitly chain exceptions

[akihironitta]

What does this PR do?

Motivation

Fixes and closes #3679.

Description of the changes

I changed lines where raiseing an exception in except to either:

1. raise .. from e to explicitly chain exceptions where the exception e has valuable information and seems useful for users.
2. raise .. from None to unchain exceptions where the previous exception has no valuable information and seems noisy and redundant. <- There were no places where this option is applicable in my opinion.

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[codecov]

Codecov Report

Merging #3750 into master will increase coverage by 3%.
The diff coverage is 43%.

@@           Coverage Diff           @@
##           master   #3750    +/-   ##
=======================================
+ Coverage      87%     90%    +3%     
=======================================
  Files         110     110            
  Lines        8858    8730   -128     
=======================================
+ Hits         7731    7842   +111     
+ Misses       1127     888   -239     

[akihironitta]

I see CI failing but I believe these errors are caused not due to the changes I made.

[Borda]

LGTM

[SkafteNicki]

LGTM, just two suggestions to be consistent with the naming

[mergify]

This pull request is now in conflict... :(

[rohitgr7]

@akihironitta have you checked if there are no more such places where this needs to be updated?

[akihironitta]

@rohitgr7 Yes, I believe. When exceptions are raised in except, they are very likely to try to make their previous exceptions more user-friendly or descriptive, so I listed and checked all the lines where exceptions are raised in except clauses with this script.

Below is the list of all lines containing raise in except:

tests/base/models.py#L15
pytorch_lightning/metrics/metric.py#L176
pytorch_lightning/accelerators/ddp2_backend.py#L52
pytorch_lightning/trainer/logging.py#L148
pytorch_lightning/tuner/batch_size_scaling.py#L185
pytorch_lightning/tuner/batch_size_scaling.py#L231
pytorch_lightning/utilities/parsing.py#L162

[rohitgr7]

Nice!