chore: import upstream snapshot with attribution

easygraph/readwrite/graphviz.py

@@ -0,0 +1,180 @@
+import easygraph as eg
+
+
+__all__ = ["write_dot", "read_dot", "from_agraph", "to_agraph"]
+
+
+def from_agraph(A, create_using=None):
+    """Returns a EasyGraph Graph or DiGraph from a PyGraphviz graph.
+
+    Parameters
+    ----------
+    A : PyGraphviz AGraph
+      A graph created with PyGraphviz
+
+    create_using : EasyGraph graph constructor, optional (default=None)
+       Graph type to create. If graph instance, then cleared before populated.
+       If `None`, then the appropriate Graph type is inferred from `A`.
+
+    Examples
+    --------
+    >>> K5 = eg.complete_graph(5)
+    >>> A = eg.to_agraph(K5)
+    >>> G = eg.from_agraph(A)
+
+    Notes
+    -----
+    The Graph G will have a dictionary G.graph_attr containing
+    the default graphviz attributes for graphs, nodes and edges.
+
+    Default node attributes will be in the dictionary G.node_attr
+    which is keyed by node.
+
+    Edge attributes will be returned as edge data in G.  With
+    edge_attr=False the edge data will be the Graphviz edge weight
+    attribute or the value 1 if no edge weight attribute is found.
+
+    """
+    if create_using is None:
+        if A.is_directed():
+            if A.is_strict():
+                create_using = eg.DiGraph
+            else:
+                create_using = eg.MultiDiGraph
+        else:
+            if A.is_strict():
+                create_using = eg.Graph
+            else:
+                create_using = eg.MultiGraph
+
+    # assign defaults
+    N = eg.empty_graph(0, create_using)
+    if A.name is not None:
+        N.name = A.name
+
+    # add graph attributes
+    N.graph.update(A.graph_attr)
+
+    # add nodes, attributes to N.node_attr
+    for n in A.nodes():
+        str_attr = {str(k): v for k, v in n.attr.items()}
+        N.add_node(str(n), **str_attr)
+
+    # add edges, assign edge data as dictionary of attributes
+    for e in A.edges():
+        u, v = str(e[0]), str(e[1])
+        attr = dict(e.attr)
+        str_attr = {str(k): v for k, v in attr.items()}
+        if not N.is_multigraph():
+            if e.name is not None:
+                str_attr["key"] = e.name
+            N.add_edge(u, v, **str_attr)
+        else:
+            N.add_edge(u, v, key=e.name, **str_attr)
+
+    # add default attributes for graph, nodes, and edges
+    # hang them on N.graph_attr
+    N.graph["graph"] = dict(A.graph_attr)
+    N.graph["node"] = dict(A.node_attr)
+    N.graph["edge"] = dict(A.edge_attr)
+    return N
+
+
+def to_agraph(N):
+    """Returns a pygraphviz graph from a EasyGraph graph N.
+
+    Parameters
+    ----------
+    N : EasyGraph graph
+      A graph created with EasyGraph
+
+    Examples
+    --------
+    >>> K5 = eg.complete_graph(5)
+    >>> A = eg.to_agraph(K5)
+
+    Notes
+    -----
+    If N has an dict N.graph_attr an attempt will be made first
+    to copy properties attached to the graph (see from_agraph)
+    and then updated with the calling arguments if any.
+
+    """
+    try:
+        import pygraphviz
+    except ImportError as err:
+        raise ImportError("requires pygraphviz http://pygraphviz.github.io/") from err
+    directed = N.is_directed()
+    strict = eg.number_of_selfloops(N) == 0 and not N.is_multigraph()
+    A = pygraphviz.AGraph(name=N.name, strict=strict, directed=directed)
+
+    # default graph attributes
+    A.graph_attr.update(N.graph.get("graph", {}))
+    A.node_attr.update(N.graph.get("node", {}))
+    A.edge_attr.update(N.graph.get("edge", {}))
+
+    A.graph_attr.update(
+        (k, v) for k, v in N.graph.items() if k not in ("graph", "node", "edge")
+    )
+
+    # add nodes
+    for n, nodedata in N.nodes.items():
+        A.add_node(n)
+        # Add node data
+        a = A.get_node(n)
+        a.attr.update({k: str(v) for k, v in nodedata.items()})
+
+    # loop over edges
+    if N.is_multigraph():
+        for u, v, key, edgedata in N.edges:
+            str_edgedata = {k: str(v) for k, v in edgedata.items() if k != "key"}
+            A.add_edge(u, v, key=str(key))
+            # Add edge data
+            a = A.get_edge(u, v)
+            a.attr.update(str_edgedata)
+
+    else:
+        for u, v, edgedata in N.edges:
+            str_edgedata = {k: str(v) for k, v in edgedata.items()}
+            A.add_edge(u, v)
+            # Add edge data
+            a = A.get_edge(u, v)
+            a.attr.update(str_edgedata)
+
+    return A
+
+
+def write_dot(G, path):
+    """Write EasyGraph graph G to Graphviz dot format on path.
+
+    Parameters
+    ----------
+    G : graph
+       A easygraph graph
+    path : filename
+       Filename or file handle to write
+    """
+    A = to_agraph(G)
+    A.write(path)
+    A.clear()
+    return
+
+
+def read_dot(path):
+    """Returns a EasyGraph graph from a dot file on path.
+
+    Parameters
+    ----------
+    path : file or string
+       File name or file handle to read.
+    """
+    try:
+        import pygraphviz
+    except ImportError as err:
+        raise ImportError(
+            "read_dot() requires pygraphviz http://pygraphviz.github.io/"
+        ) from err
+    A = pygraphviz.AGraph(file=path)
+    gr = from_agraph(A)
+    A.clear()
+    return gr