introduced hidden edges to not create cycles in the graph (#20)

src/openeo_pg_parser/graph.py

@@ -204,10 +204,10 @@ def __eq__(self, other):
         return self.id == other.id
 
 
-class Edge(object):
+class Edge:
     """ An edge connects two nodes. The connection has a label/name. """
 
-    def __init__(self, id=None, name=None, nodes=None):
+    def __init__(self, id=None, name=None, nodes=None, hidden=False):
         """
         Constructor of `graph.Edge`.
 
@@ -219,6 +219,8 @@ def __init__(self, id=None, name=None, nodes=None):
             Name of the edge/connection.
         nodes : list of graph.Nodes, optional
             List containing two nodes comprising an edge.
+        hidden : bool, optional
+            True if edge should be ignored, e.g. for sorting (defaults to False).
         """
 
         if nodes is not None:
@@ -230,6 +232,7 @@ def __init__(self, id=None, name=None, nodes=None):
         self.id = id
         self.name = name
         self.nodes = nodes
+        self.hidden = hidden
 
     @property
     def node_ids(self):
@@ -256,7 +259,7 @@ def __eq__(self, other):
                (self.name == other.name)
 
 
-class Graph(object):
+class Graph:
     """ Represents an arbitrary graph containing `graph.Node` instances as nodes. """
 
     def __init__(self, nodes):
@@ -585,7 +588,7 @@ def to_igraph(self):
         edges = []
         for node in self.nodes:
             for edge in node.edges:
-                if edge not in edges:
+                if not edge.hidden and edge not in edges:
                     # ignore nodes, which are not contained in the graph
                     if edge.nodes[0].id not in self.ids or edge.nodes[1].id not in self.ids:
                         continue

src/openeo_pg_parser/translate.py

@@ -146,7 +146,7 @@ def adjust_from_nodes(process_graph):
     return process_graph
 
 
-def create_edge(node_from, node_to, name="data"):
+def create_edge(node_from, node_to, name="data", hidden=False):
     """
     Creates a directed edge of type `graph.Edge` between the nodes `node_from` and `node_to`.
 
@@ -158,6 +158,8 @@ def create_edge(node_from, node_to, name="data"):
         End node of the edge.
     name : str, optional
         Name of the edge (default is "data")
+    hidden : bool, optional
+            True if edge should be ignored, e.g. for sorting (defaults to False).
 
     Returns
     -------
@@ -167,7 +169,7 @@ def create_edge(node_from, node_to, name="data"):
     """
     edge_nodes = [node_from, node_to]
     edge_id = "_".join([edge_node.id for edge_node in edge_nodes])
-    edge = Edge(id=edge_id, name=name, nodes=edge_nodes)
+    edge = Edge(id=edge_id, name=name, nodes=edge_nodes, hidden=hidden)
     node_to.add_edge(edge)
     node_from.add_edge(edge)
 
@@ -212,7 +214,7 @@ def adjust_from_parameters(process_graph, parameters=None):
                     node_relatives = parent_node.relatives(link="data", ancestor=True)
                     # parameter is required, but the start node has no input data -> take parent node as data reference
                     if parameter.is_required and not node_relatives:
-                        create_edge(parent_node, node)
+                        create_edge(parent_node, node, hidden=True)
                         node_argument = {'from_node': '{}'.format(parent_node.id)}
                         set_obj_elem_from_keys(node.content['arguments'], key_lineage[:-1], node_argument)
                     # parameter is required and parent node has input data -> add all data relatives of parent node later