improve comments in topological sort

Author: dimitri-yatsenko

datajoint/dependencies.py

@@ -42,7 +42,8 @@ def topo_sort(graph):
         if (master := extract_master(part)) in graph:
             for edge in graph.in_edges(part):
                 parent = edge[0]
-                if parent != master and extract_master(parent) != master:
+                if master not in (parent, extract_master(parent)):
+                    # if parent is neither master nor part of master
                     graph.add_edge(parent, master)
     sorted_nodes = list(nx.topological_sort(graph))
 

datajoint/diagram.py

@@ -71,7 +71,7 @@ class Diagram(nx.DiGraph):
         Only those tables that are loaded in the connection object are displayed
         """
 
-        def __init__(self, source=None, context=None):
+        def __init__(self, source, context=None):
 
             if isinstance(source, Diagram):
                 # copy constructor