Fix some spacing

official/mnist/dataset.py

@@ -33,7 +33,7 @@ def read32(bytestream):
 
 def check_image_file_header(filename):
   """Validate that filename corresponds to images for the MNIST dataset."""
-  with tf.gfile.Open(filename,'rb') as f:
+  with tf.gfile.Open(filename, 'rb') as f:
     magic = read32(f)
     num_images = read32(f)
     rows = read32(f)
@@ -49,7 +49,7 @@ def check_image_file_header(filename):
 
 def check_labels_file_header(filename):
   """Validate that filename corresponds to labels for the MNIST dataset."""
-  with tf.gfile.Open(filename,'rb') as f:
+  with tf.gfile.Open(filename, 'rb') as f:
     magic = read32(f)
     num_items = read32(f)
     if magic != 2049:
@@ -58,7 +58,7 @@ def check_labels_file_header(filename):
 
 
 def download(directory, filename):
-  """Download (and unzip) a file from the MNIST dataset, if it doesn't already exist."""
+  """Download (and unzip) a file from the MNIST dataset if not already done."""
   filepath = os.path.join(directory, filename)
   if tf.gfile.Exists(filepath):
     return filepath