ref: inner train loop (intermediate step) 10/n

[williamFalcon]

No description provided.

[pep8speaks]

Hello @williamFalcon! Thanks for opening this PR.

• In the file pytorch_lightning/trainer/training_loop.py:

Line 817:21: E731 do not assign a lambda expression, use a def

Do see the Hitchhiker's guide to code style

[codecov]

Codecov Report

Merging #3369 into master will increase coverage by 4%.
The diff coverage is 79%.

@@           Coverage Diff           @@
##           master   #3369    +/-   ##
=======================================
+ Coverage      86%     90%    +4%     
=======================================
  Files          93      93            
  Lines        8244    8321    +77     
=======================================
+ Hits         7056    7456   +400     
+ Misses       1188     865   -323