ADD file via upload

ema.py

@@ -0,0 +1,22 @@
+from typing import Optional
+
+
+class EMAValue(object):
+    def __init__(self, init_value: Optional[float] = None, decay_factor: float = 0.999) -> None:
+        super().__init__()
+        self._value = init_value
+        self._decay_factor = decay_factor
+
+    @property
+    def value(self) -> Optional[float]:
+        return self._value
+
+    def update(self, value: float) -> None:
+        if self._value is None:
+            self._value = value
+        else:
+            self._value = self._decay_factor * self._value + (1 - self._decay_factor) * value
+
+    def update_with_return(self, value: float) -> Optional[float]:
+        self.update(value)
+        return self._value