Add shape property and equality operation to LazyFrames (#1862)

* Add shape property and equality operation to LazyFrames for simplified usage in tests

* Fix shape property with lz4_compress

gym/wrappers/frame_stack.py

@@ -2,7 +2,7 @@ from collections import deque
 import numpy as np
 
 from gym.spaces import Box
-from gym import ObservationWrapper
+from gym import Wrapper
 
 
 class LazyFrames(object):
@@ -19,7 +19,7 @@ class LazyFrames(object):
     def __init__(self, frames, lz4_compress=False):
         if lz4_compress:
             from lz4.block import compress
-            self.shape = frames[0].shape
+            self.frame_shape = frames[0].shape
             self.dtype = frames[0].dtype
             frames = [compress(frame) for frame in frames]
         self._frames = frames
@@ -28,7 +28,7 @@ class LazyFrames(object):
     def __array__(self, dtype=None):
         if self.lz4_compress:
             from lz4.block import decompress
-            frames = [np.frombuffer(decompress(frame), dtype=self.dtype).reshape(self.shape) for frame in self._frames]
+            frames = [np.frombuffer(decompress(frame), dtype=self.dtype).reshape(self.frame_shape) for frame in self._frames]
         else:
             frames = self._frames
         out = np.stack(frames, axis=0)
@@ -42,8 +42,15 @@ class LazyFrames(object):
     def __getitem__(self, i):
         return self.__array__()[i]
 
+    def __eq__(self, other):
+        return self.__array__() == other
 
-class FrameStack(ObservationWrapper):
+    @property
+    def shape(self):
+        return self.__array__().shape
+
+
+class FrameStack(Wrapper):
     r"""Observation wrapper that stacks the observations in a rolling manner. 
 
     For example, if the number of stacks is 4, then the returned observation contains