None check for filepath in ModelCheckpoint (Lightning-AI#1654)

Check if the optional filepath is None before checking if it exists

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: yukw777

CHANGELOG.md

@@ -16,11 +16,13 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
+- Fixed ModelCheckpoint not None checking filepath ([1654](https://github.com/PyTorchLightning/pytorch-lightning/pull/1654))
+
 
 ## [0.7.5] - 2020-04-27
 
 ### Changed
- 
+
 - Allow logging of metrics together with `hparams` ([#1630](https://github.com/PyTorchLightning/pytorch-lightning/pull/1630))
 - Allow metrics logged together with hparams ([#1630](https://github.com/PyTorchLightning/pytorch-lightning/pull/1630))
 
@@ -51,7 +53,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added `ddp_cpu` backend for testing ddp without GPUs ([#1158](https://github.com/PyTorchLightning/pytorch-lightning/pull/1158))
 - Added [Horovod](http://horovod.ai) support as a distributed backend `Trainer(distributed_backend='horovod')` ([#1529](https://github.com/PyTorchLightning/pytorch-lightning/pull/1529))
 - Added support for 8 core distributed training on Kaggle TPU's ([#1568](https://github.com/PyTorchLightning/pytorch-lightning/pull/1568))
-- Added support for native AMP ([#1561](https://github.com/PyTorchLightning/pytorch-lightning/pull/1561), [#1580](https://github.com/PyTorchLightning/pytorch-lightning/pull/1580)) 
+- Added support for native AMP ([#1561](https://github.com/PyTorchLightning/pytorch-lightning/pull/1561), [#1580](https://github.com/PyTorchLightning/pytorch-lightning/pull/1580))
 
 ### Changed
 
@@ -78,7 +80,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed loggers - flushing last logged metrics even before continue, e.g. `trainer.test()` results ([#1459](https://github.com/PyTorchLightning/pytorch-lightning/pull/1459))
 - Fixed optimizer configuration when `configure_optimizers` returns dict without `lr_scheduler` ([#1443](https://github.com/PyTorchLightning/pytorch-lightning/pull/1443))
 - Fixed `LightningModule` - mixing hparams and arguments in `LightningModule.__init__()` crashes load_from_checkpoint() ([#1505](https://github.com/PyTorchLightning/pytorch-lightning/pull/1505))
-- Added a missing call to the `on_before_zero_grad` model hook ([#1493](https://github.com/PyTorchLightning/pytorch-lightning/pull/1493)). 
+- Added a missing call to the `on_before_zero_grad` model hook ([#1493](https://github.com/PyTorchLightning/pytorch-lightning/pull/1493)).
 - Allow use of sweeps with `WandbLogger` ([#1512](https://github.com/PyTorchLightning/pytorch-lightning/pull/1512))
 - Fixed a bug that caused the `callbacks` Trainer argument to reference a global variable ([#1534](https://github.com/PyTorchLightning/pytorch-lightning/pull/1534)).
 - Fixed a bug that set all boolean CLI arguments from `Trainer.add_argparse_args` always to True ([#1571](https://github.com/PyTorchLightning/pytorch-lightning/pull/1571))

pytorch_lightning/callbacks/model_checkpoint.py

@@ -86,7 +86,7 @@ def __init__(self, filepath: Optional[str] = None, monitor: str = 'val_loss', ve
                  save_top_k: int = 1, save_weights_only: bool = False,
                  mode: str = 'auto', period: int = 1, prefix: str = ''):
         super().__init__()
-        if save_top_k > 0 and os.path.isdir(filepath) and len(os.listdir(filepath)) > 0:
+        if save_top_k > 0 and filepath is not None and os.path.isdir(filepath) and len(os.listdir(filepath)) > 0:
             rank_zero_warn(
                 f"Checkpoint directory {filepath} exists and is not empty with save_top_k != 0."
                 "All files in this directory will be deleted when a checkpoint is saved!"

tests/callbacks/test_callbacks.py

@@ -1,3 +1,4 @@
+import pytest
 import tests.base.utils as tutils
 from pytorch_lightning import Callback
 from pytorch_lightning import Trainer, LightningModule
@@ -249,7 +250,8 @@ def test_pickling(tmpdir):
     pickle.dumps(early_stopping)
 
 
-def test_model_checkpoint_with_non_string_input(tmpdir):
+@pytest.mark.parametrize('save_top_k', [-1, 0, 1, 2])
+def test_model_checkpoint_with_non_string_input(tmpdir, save_top_k):
     """ Test that None in checkpoint callback is valid and that chkp_path is
         set correctly """
     tutils.reset_seed()
@@ -260,7 +262,7 @@ class CurrentTestModel(LightTrainDataloader, TestModelBase):
     hparams = tutils.get_default_hparams()
     model = CurrentTestModel(hparams)
 
-    checkpoint = ModelCheckpoint(filepath=None, save_top_k=-1)
+    checkpoint = ModelCheckpoint(filepath=None, save_top_k=save_top_k)
 
     trainer = Trainer(default_root_dir=tmpdir,
                       checkpoint_callback=checkpoint,