fixing bug in testing for IterableDataset (#547)

Author: MikeScarp

pytorch_lightning/trainer/data_loading_mixin.py

@@ -24,7 +24,7 @@ def init_train_dataloader(self, model):
  self.get_train_dataloader = model.train_dataloader
 
  # determine number of training batches
- if isinstance(self.get_train_dataloader(), IterableDataset):
+ if isinstance(self.get_train_dataloader().dataset, IterableDataset):
  self.nb_training_batches = float('inf')
  else:
  self.nb_training_batches = len(self.get_train_dataloader())
@@ -167,7 +167,7 @@ def get_dataloaders(self, model):
  self.get_val_dataloaders()
 
  # support IterableDataset for train data
- self.is_iterable_train_dataloader = isinstance(self.get_train_dataloader(), IterableDataset)
+ self.is_iterable_train_dataloader = isinstance(self.get_train_dataloader().dataset, IterableDataset)
  if self.is_iterable_train_dataloader and not isinstance(self.val_check_interval, int):
  m = '''
  When using an iterableDataset for train_dataloader,