Fix reset TensorRunningAccum (#5106)

* Fix reset TensorRunningAccum

* add test for TensorRunningAccum's reset method

* fix CI failed due to PEP8

Co-authored-by: Rohit Gupta <rohitgr1998@gmail.com>

pytorch_lightning/trainer/supporters.py

@@ -56,7 +56,7 @@ class TensorRunningAccum(object):
 
     def reset(self) -> None:
         """Empty the accumulator."""
-        self = TensorRunningAccum(self.window_length)
+        self.__init__(self.window_length)
 
     def last(self):
         """Get the last added element."""

tests/trainer/test_supporters.py

@@ -17,10 +17,33 @@ import pytest
 import torch
 
 from torch.utils.data import TensorDataset
-from pytorch_lightning.trainer.supporters import CycleIterator, CombinedLoader, CombinedDataset, CombinedLoaderIterator
+from pytorch_lightning.trainer.supporters import (
+    CycleIterator, CombinedLoader, CombinedDataset, CombinedLoaderIterator, TensorRunningAccum)
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 
 
+
+def test_tensor_running_accum_reset():
+    """ Test that reset would set all attributes to the initialization state """
+
+    window_length = 10
+
+    accum = TensorRunningAccum(window_length=window_length)
+    assert accum.last() is None
+    assert accum.mean() is None
+
+    accum.append(torch.tensor(1.5))
+    assert accum.last() == torch.tensor(1.5)
+    assert accum.mean() == torch.tensor(1.5)
+
+    accum.reset()
+    assert accum.window_length == window_length
+    assert accum.memory is None
+    assert accum.current_idx == 0
+    assert accum.last_idx is None
+    assert not accum.rotated
+
+
 def test_cycle_iterator():
     """Test the cycling function of `CycleIterator`"""
     iterator = CycleIterator(range(100), 1000)