### diff env/lib/python3.9/site-packages/networkx/algorithms/traversal/edgedfs.py @ 0:4f3585e2f14bdraftdefaulttip

"planemo upload commit 60cee0fc7c0cda8592644e1aad72851dec82c959"
author shellac Mon, 22 Mar 2021 18:12:50 +0000
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```--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.9/site-packages/networkx/algorithms/traversal/edgedfs.py	Mon Mar 22 18:12:50 2021 +0000
@@ -0,0 +1,174 @@
+"""
+===========================
+Depth First Search on Edges
+===========================
+
+Algorithms for a depth-first traversal of edges in a graph.
+
+"""
+import networkx as nx
+
+FORWARD = "forward"
+REVERSE = "reverse"
+
+__all__ = ["edge_dfs"]
+
+
+def edge_dfs(G, source=None, orientation=None):
+    """A directed, depth-first-search of edges in `G`, beginning at `source`.
+
+    Yield the edges of G in a depth-first-search order continuing until
+    all edges are generated.
+
+    Parameters
+    ----------
+    G : graph
+        A directed/undirected graph/multigraph.
+
+    source : node, list of nodes
+        The node from which the traversal begins. If None, then a source
+        is chosen arbitrarily and repeatedly until all edges from each node in
+        the graph are searched.
+
+    orientation : None | 'original' | 'reverse' | 'ignore' (default: None)
+        For directed graphs and directed multigraphs, edge traversals need not
+        respect the original orientation of the edges.
+        When set to 'reverse' every edge is traversed in the reverse direction.
+        When set to 'ignore', every edge is treated as undirected.
+        When set to 'original', every edge is treated as directed.
+        In all three cases, the yielded edge tuples add a last entry to
+        indicate the direction in which that edge was traversed.
+        If orientation is None, the yielded edge has no direction indicated.
+        The direction is respected, but not reported.
+
+    Yields
+    ------
+    edge : directed edge
+        A directed edge indicating the path taken by the depth-first traversal.
+        For graphs, `edge` is of the form `(u, v)` where `u` and `v`
+        are the tail and head of the edge as determined by the traversal.
+        For multigraphs, `edge` is of the form `(u, v, key)`, where `key` is
+        the key of the edge. When the graph is directed, then `u` and `v`
+        are always in the order of the actual directed edge.
+        If orientation is not None then the edge tuple is extended to include
+        the direction of traversal ('forward' or 'reverse') on that edge.
+
+    Examples
+    --------
+    >>> nodes = [0, 1, 2, 3]
+    >>> edges = [(0, 1), (1, 0), (1, 0), (2, 1), (3, 1)]
+
+    >>> list(nx.edge_dfs(nx.Graph(edges), nodes))
+    [(0, 1), (1, 2), (1, 3)]
+
+    >>> list(nx.edge_dfs(nx.DiGraph(edges), nodes))
+    [(0, 1), (1, 0), (2, 1), (3, 1)]
+
+    >>> list(nx.edge_dfs(nx.MultiGraph(edges), nodes))
+    [(0, 1, 0), (1, 0, 1), (0, 1, 2), (1, 2, 0), (1, 3, 0)]
+
+    >>> list(nx.edge_dfs(nx.MultiDiGraph(edges), nodes))
+    [(0, 1, 0), (1, 0, 0), (1, 0, 1), (2, 1, 0), (3, 1, 0)]
+
+    >>> list(nx.edge_dfs(nx.DiGraph(edges), nodes, orientation="ignore"))
+    [(0, 1, 'forward'), (1, 0, 'forward'), (2, 1, 'reverse'), (3, 1, 'reverse')]
+
+    >>> list(nx.edge_dfs(nx.MultiDiGraph(edges), nodes, orientation="ignore"))
+    [(0, 1, 0, 'forward'), (1, 0, 0, 'forward'), (1, 0, 1, 'reverse'), (2, 1, 0, 'reverse'), (3, 1, 0, 'reverse')]
+
+    Notes
+    -----
+    The goal of this function is to visit edges. It differs from the more
+    familiar depth-first traversal of nodes, as provided by
+    :func:`networkx.algorithms.traversal.depth_first_search.dfs_edges`, in
+    that it does not stop once every node has been visited. In a directed graph
+    with edges [(0, 1), (1, 2), (2, 1)], the edge (2, 1) would not be visited
+    if not for the functionality provided by this function.
+
+    See Also
+    --------
+    dfs_edges
+
+    """
+    nodes = list(G.nbunch_iter(source))
+    if not nodes:
+        return
+
+    directed = G.is_directed()
+    kwds = {"data": False}
+    if G.is_multigraph() is True:
+        kwds["keys"] = True
+
+    # set up edge lookup
+    if orientation is None:
+
+        def edges_from(node):
+            return iter(G.edges(node, **kwds))
+
+    elif not directed or orientation == "original":
+
+        def edges_from(node):
+            for e in G.edges(node, **kwds):
+                yield e + (FORWARD,)
+
+    elif orientation == "reverse":
+
+        def edges_from(node):
+            for e in G.in_edges(node, **kwds):
+                yield e + (REVERSE,)
+
+    elif orientation == "ignore":
+
+        def edges_from(node):
+            for e in G.edges(node, **kwds):
+                yield e + (FORWARD,)
+            for e in G.in_edges(node, **kwds):
+                yield e + (REVERSE,)
+
+    else:
+        raise nx.NetworkXError("invalid orientation argument.")
+
+    # set up formation of edge_id to easily look up if edge already returned
+    if directed:
+
+        def edge_id(edge):
+            # remove direction indicator
+            return edge[:-1] if orientation is not None else edge
+
+    else:
+
+        def edge_id(edge):
+            # single id for undirected requires frozenset on nodes
+            return (frozenset(edge[:2]),) + edge[2:]
+
+    # Basic setup
+    check_reverse = directed and orientation in ("reverse", "ignore")
+
+    visited_edges = set()
+    visited_nodes = set()
+    edges = {}
+
+    # start DFS
+    for start_node in nodes:
+        stack = [start_node]
+        while stack:
+            current_node = stack[-1]
+            if current_node not in visited_nodes:
+                edges[current_node] = edges_from(current_node)
+                visited_nodes.add(current_node)
+
+            try:
+                edge = next(edges[current_node])
+            except StopIteration:
+                # No more edges from the current node.
+                stack.pop()
+            else:
+                edgeid = edge_id(edge)
+                if edgeid not in visited_edges:
+                    visited_edges.add(edgeid)
+                    # Mark the traversed "to" node as to-be-explored.
+                    if check_reverse and edge[-1] == REVERSE:
+                        stack.append(edge[0])
+                    else:
+                        stack.append(edge[1])
+                    yield edge```