Simplify, expand and explain complicated loops in dag.py

depau · depau · commit 861980db0bd6 · 2018-01-09T15:47:09.000+01:00
diff --git a/ffmpeg/dag.py b/ffmpeg/dag.py
@@ -75,8 +75,10 @@ def incoming_edge_map(self):
 
 def get_incoming_edges(downstream_node, incoming_edge_map):
     edges = []
-    for downstream_label, upstream_info in [(i[0], i[1]) for i in incoming_edge_map.items()]:
+    for downstream_label, upstream_info in incoming_edge_map.items():
+        # `upstream_info` may contain the upstream_selector. [:2] trims it away
         upstream_node, upstream_label = upstream_info[:2]
+        # Take into account the stream selector if it's present (i.e. len(upstream_info) >= 3)
         upstream_selector = None if len(upstream_info) < 3 else upstream_info[2]
         edges += [DagEdge(downstream_node, downstream_label, upstream_node, upstream_label, upstream_selector)]
     return edges
@@ -86,7 +88,9 @@ def get_outgoing_edges(upstream_node, outgoing_edge_map):
     edges = []
     for upstream_label, downstream_infos in list(outgoing_edge_map.items()):
         for downstream_info in downstream_infos:
+            # `downstream_info` may contain the downstream_selector. [:2] trims it away
             downstream_node, downstream_label = downstream_info[:2]
+            # Take into account the stream selector if it's present
             downstream_selector = None if len(downstream_info) < 3 else downstream_info[2]
             edges += [DagEdge(downstream_node, downstream_label, upstream_node, upstream_label, downstream_selector)]
     return edges
@@ -99,8 +103,10 @@ class KwargReprNode(DagNode):
     @property
     def __upstream_hashes(self):
         hashes = []
-        # This is needed to allow extra stuff in the incoming_edge_map's value tuples
-        for downstream_label, (upstream_node, upstream_label) in [(i[0], i[1][:2]) for i in self.incoming_edge_map.items()]:
+        for downstream_label, upstream_info in self.incoming_edge_map.items():
+            # `upstream_info` may contain the upstream_selector. [:2] trims it away
+            upstream_node, upstream_label = upstream_info[:2]
+            # The stream selector is discarded when calculating the hash: the stream "as a whole" is still the same
             hashes += [hash(x) for x in [downstream_label, upstream_node, upstream_label]]
         return hashes
 
