bugfix: batch_size for MNISTDataModule (#331)

* bugfix: batch_size for MNISTDataModule

* fix MNISTDataModule *_dataloader() signatures

pl_bolts/datamodules/mnist_datamodule.py

@@ -76,6 +76,7 @@ def __init__(
         self.num_workers = num_workers
         self.normalize = normalize
         self.seed = seed
+        self.batch_size = batch_size
 
     @property
     def num_classes(self):
@@ -92,15 +93,14 @@ def prepare_data(self):
         MNIST(self.data_dir, train=True, download=True, transform=transform_lib.ToTensor())
         MNIST(self.data_dir, train=False, download=True, transform=transform_lib.ToTensor())
 
-    def train_dataloader(self, batch_size=32, transforms=None):
+    def train_dataloader(self):
         """
         MNIST train set removes a subset to use for validation
 
         Args:
-            batch_size: size of batch
             transforms: custom transforms
         """
-        transforms = transforms or self.train_transforms or self._default_transforms()
+        transforms = self.default_transforms() if self.train_transforms is None else self.train_transforms
 
         dataset = MNIST(self.data_dir, train=True, download=False, transform=transforms)
         train_length = len(dataset)
@@ -109,55 +109,54 @@ def train_dataloader(self, batch_size=32, transforms=None):
         )
         loader = DataLoader(
             dataset_train,
-            batch_size=batch_size,
+            batch_size=self.batch_size,
             shuffle=True,
             num_workers=self.num_workers,
             drop_last=True,
             pin_memory=True,
         )
         return loader
 
-    def val_dataloader(self, batch_size=32, transforms=None):
+    def val_dataloader(self):
         """
         MNIST val set uses a subset of the training set for validation
 
         Args:
-            batch_size: size of batch
             transforms: custom transforms
         """
-        transforms = transforms or self.val_transforms or self._default_transforms()
+        transforms = self.default_transforms() if self.val_transforms is None else self.val_transforms
         dataset = MNIST(self.data_dir, train=True, download=False, transform=transforms)
         train_length = len(dataset)
         _, dataset_val = random_split(
             dataset, [train_length - self.val_split, self.val_split], generator=torch.Generator().manual_seed(self.seed)
         )
         loader = DataLoader(
             dataset_val,
-            batch_size=batch_size,
+            batch_size=self.batch_size,
             shuffle=False,
             num_workers=self.num_workers,
             drop_last=True,
             pin_memory=True,
         )
         return loader
 
-    def test_dataloader(self, batch_size=32, transforms=None):
+    def test_dataloader(self):
         """
         MNIST test set uses the test split
 
         Args:
-            batch_size: size of batch
             transforms: custom transforms
         """
-        transforms = transforms or self.val_transforms or self._default_transforms()
+        transforms = self.default_transforms() if self.test_transforms is None else self.test_transforms
 
         dataset = MNIST(self.data_dir, train=False, download=False, transform=transforms)
         loader = DataLoader(
-            dataset, batch_size=batch_size, shuffle=False, num_workers=self.num_workers, drop_last=True, pin_memory=True
+            dataset, batch_size=self.batch_size, shuffle=False, num_workers=self.num_workers, drop_last=True,
+            pin_memory=True
         )
         return loader
 
-    def _default_transforms(self):
+    def default_transforms(self):
         if self.normalize:
             mnist_transforms = transform_lib.Compose(
                 [transform_lib.ToTensor(), transform_lib.Normalize(mean=(0.5,), std=(0.5,))]