message: Fixed error catching over h5py versions.
diff: @@ -1287,7 +1287,7 @@ class ModelCheckpoint(Callback):
  self._maybe_remove_file()
  except IOError as e:
  # `e.errno` appears to be `None` so checking the content of `e.args[0]`.
  - if 'is a directory' in six.ensure_str(e.args[0]):
  + if 'is a directory' in six.ensure_str(e.args[0]).lower():
  raise IOError('Please specify a non-directory filepath for '
  'ModelCheckpoint. Filepath used is an existing '
  'directory: {}'.format(filepath))
  