Adds the option of saving the last model on checkpoint

[lgvaz]

Before submitting

• Was this discussed/approved via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?
• If you made a notable change (that affects users), did you update the CHANGELOG?

What does this PR do?

Implements part of #1658 , option to always save the latest model.
Fixes #1926

[pep8speaks]

Hello @lgvaz! Thanks for updating this PR.

• In the file tests/trainer/test_trainer.py:

Line 259:111: E501 line too long (113 > 110 characters)

Comment last updated at 2020-05-22 03:44:38 UTC

[lgvaz]

I thought by reading the contributing guide that the max line length was 120, bot does not like that my line is 113, should I make the bot happy?

[awaelchli]

the bot warns after 110 characters and the test will fail for >120
the intention should not be to make the bot happy, but the reader of the code :))

[awaelchli]

could you also add an entry in changelog?

[lgvaz]

Does the changelog makes sense?

[justusschock]

Do we want to expose this argument in the trainer?

[Borda]

Do we want to expose this argument in the trainer?

what do you mean, I think that it quite natural also save the last state especially when your training accidentally stops...

[lgvaz]

I think that it quite natural also save the last state

Is it a good idea to make save_last default to True?

[Borda]

I think that it quite natural also save the last state

Is it a good idea to make save_last default to True?

good point, probably False is better option since every save would slow down...
lets fix also #1926 in this PR :]

[lgvaz]

lets fix also #1926 in this PR :]

Should I do something or is it automatically going to close that once this is merged?

[Borda]

lets fix also #1926 in this PR :]

Should I do something or is it automatically going to close that once this is merged?

now it is linked and with merging this PR it will automatically close the linked issue