--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/planemo/lib/python3.7/site-packages/networkx/utils/union_find.py	Fri Jul 31 00:32:28 2020 -0400
@@ -0,0 +1,109 @@
+#    Copyright 2016-2019 NetworkX developers.
+#    Copyright (C) 2004-2019 by
+#    Aric Hagberg <hagberg@lanl.gov>
+#    Dan Schult <dschult@colgate.edu>
+#    Pieter Swart <swart@lanl.gov>
+#    All rights reserved.
+#    BSD license.
+"""
+Union-find data structure.
+"""
+
+from networkx.utils import groups
+
+
+class UnionFind:
+    """Union-find data structure.
+
+    Each unionFind instance X maintains a family of disjoint sets of
+    hashable objects, supporting the following two methods:
+
+    - X[item] returns a name for the set containing the given item.
+      Each set is named by an arbitrarily-chosen one of its members; as
+      long as the set remains unchanged it will keep the same name. If
+      the item is not yet part of a set in X, a new singleton set is
+      created for it.
+
+    - X.union(item1, item2, ...) merges the sets containing each item
+      into a single larger set.  If any item is not yet part of a set
+      in X, it is added to X as one of the members of the merged set.
+
+      Union-find data structure. Based on Josiah Carlson's code,
+      http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/215912
+      with significant additional changes by D. Eppstein.
+      http://www.ics.uci.edu/~eppstein/PADS/UnionFind.py
+
+    """
+
+    def __init__(self, elements=None):
+        """Create a new empty union-find structure.
+
+        If *elements* is an iterable, this structure will be initialized
+        with the discrete partition on the given set of elements.
+
+        """
+        if elements is None:
+            elements = ()
+        self.parents = {}
+        self.weights = {}
+        for x in elements:
+            self.weights[x] = 1
+            self.parents[x] = x
+
+    def __getitem__(self, object):
+        """Find and return the name of the set containing the object."""
+
+        # check for previously unknown object
+        if object not in self.parents:
+            self.parents[object] = object
+            self.weights[object] = 1
+            return object
+
+        # find path of objects leading to the root
+        path = [object]
+        root = self.parents[object]
+        while root != path[-1]:
+            path.append(root)
+            root = self.parents[root]
+
+        # compress the path and return
+        for ancestor in path:
+            self.parents[ancestor] = root
+        return root
+
+    def __iter__(self):
+        """Iterate through all items ever found or unioned by this structure.
+
+        """
+        return iter(self.parents)
+
+    def to_sets(self):
+        """Iterates over the sets stored in this structure.
+
+        For example::
+
+            >>> partition = UnionFind('xyz')
+            >>> sorted(map(sorted, partition.to_sets()))
+            [['x'], ['y'], ['z']]
+            >>> partition.union('x', 'y')
+            >>> sorted(map(sorted, partition.to_sets()))
+            [['x', 'y'], ['z']]
+
+        """
+        # Ensure fully pruned paths
+        for x in self.parents.keys():
+            _ = self[x] # Evaluated for side-effect only
+
+        # TODO In Python 3.3+, this should be `yield from ...`.
+        for block in groups(self.parents).values():
+            yield block
+
+    def union(self, *objects):
+        """Find the sets containing the objects and merge them all."""
+        roots = [self[x] for x in objects]
+        # Find the heaviest root according to its weight.
+        heaviest = max(roots, key=lambda r: self.weights[r])
+        for r in roots:
+            if r != heaviest:
+                self.weights[heaviest] += self.weights[r]
+                self.parents[r] = heaviest