Checking ipywidgets is installed for ensure tqdm working

[olineumann]

What does this PR do?

Some users having problems with the progress bar in combination with jupyter notebook/lab. Sometimes it crashes because of missing dependencies, sometimes the progress bar isn't displayed correctly. Normally tqdm should select the correct package via tqdm.auto which is used in the code, but as some users reporting (not only in pytorch_lightning) it seems not working correctly.

Since pytorch_lightning doesn't want to add ipywidgets (which often is the problem) to the dependencies it would be better to check if this package is installed before importing tqdm.auto and import only tqdm of not.

As an example run this in jupyter without ipywidgets installed:

import time

# this will fail
from tqdm.auto import tqdm

# this not
#try:
#    import ipywidgets
#    from tqdm.auto import tqdm
#except ImportError as e:
#    from tqdm import tqdm

for i in tqdm(range(1000)):
    time.sleep(0.01)

Fixes #1687

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• Did you write any new necessary tests?
  Not needed I think?
• Did you verify new and existing tests pass locally with your changes?
  Tests passed locally.
• If you made a notable change (that affects users), did you update the CHANGELOG?
  Not necessary.

PR review

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[olineumann]

Just searched for tqdm.auto imports and replaced it. I think in progress.py it is correct in lr_finder.py I'm not sure and I'm wondering why lr_finder doesn't use ProgressBar?

[awaelchli]

Nice!

[awaelchli]

could we use

import importlib 
if importlib.util.find_spec("ipywidgets") is not None:
    import ipywidgets
    from tqdm.auto import tqdm
else:
    from tqdm import tqdm

? (brain compiled, may have typos)
ImportError is not suitable here in general.

[awaelchli]

should probably also add "pragma no cover " not to decrease coverage

[olineumann]

Yes, sure. Thanks!

[codecov]

Codecov Report

Merging #2417 into master will decrease coverage by 0%.
The diff coverage is 78%.

@@          Coverage Diff           @@
##           master   #2417   +/-   ##
======================================
- Coverage      89%     89%   -0%     
======================================
  Files          69      69           
  Lines        5476    5482    +6     
======================================
+ Hits         4856    4860    +4     
- Misses        620     622    +2     

[mergify]

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

[williamFalcon]

@olineumann love the PR! this is a great addition