Fix mypy 0.800 plus when prepending $PYTHONPATH to sys.path (#5698)

* Fix mypy when prepending $PYTHONPATH to sys.path

* attempt mypy fix

* Revert "attempt mypy fix"

This reverts commit fb7ed82.

* fix mypy

Co-authored-by: Jirka Borovec <jirka.borovec@seznam.cz>

.github/workflows/code-formatting.yml

@@ -69,7 +69,7 @@ jobs:
           python-version: 3.8
       - name: Install mypy
         run: |
-          pip install "mypy==0.790"
+          pip install mypy==0.790
           pip list
       - name: mypy check
         run: |

tests/models/data/__init__.py

@@ -0,0 +1 @@
+# this is needed only for mypy==0.800 as it undestands only packages

tests/models/data/horovod/__init__.py

@@ -0,0 +1 @@
+# this is needed only for mypy==0.800 as it undestands only packages

tests/models/data/horovod/train_default_model.py

@@ -21,10 +21,10 @@
 import os
 import sys
 
-# this is need as e.g. Conda do not uses `PYTHONPATH` env var as pip or/and virtualenv
-from pytorch_lightning.trainer.states import TrainerState
-
-sys.path = os.getenv('PYTHONPATH').split(':') + sys.path
+# this is needed because Conda does not use `PYTHONPATH` env var while pip and virtualenv do
+PYTHONPATH = os.getenv('PYTHONPATH', '')
+if ':' in PYTHONPATH:
+    sys.path = PYTHONPATH.split(':') + sys.path
 
 from pytorch_lightning import Trainer  # noqa: E402
 from pytorch_lightning.callbacks import ModelCheckpoint  # noqa: E402