Check objects type rather than None for deps and properties

 * this allow subclasses working without clients to override the
   _get_pom_factory method and return plain artifacts from coordinates
   rather than full Pom objects when there is no client to retrieve an
   artifact remotely.

Link: sassoftware#3
Link: sassoftware#4

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

pymaven/pom.py

@@ -278,7 +278,7 @@ def dependencies(self):
         dependencies = {}
 
         # we depend on our parent
-        if self.parent is not None:
+        if isinstance(self.parent, Pom):
             group = self.parent.group_id
             artifact = self.parent.artifact_id
             version = self.parent.version
@@ -305,7 +305,7 @@ def dependency_management(self):
         dep_mgmt = {}
 
         # add parent's block first so we can override it
-        if self.parent is not None:
+        if isinstance(self.parent, Pom):
             dep_mgmt.update(self.parent.dependency_management)
 
         dep_mgmt.update(self._find_dependency_management())
@@ -329,8 +329,9 @@ def parent(self):
     def properties(self):
         properties = {}
 
-        if self.parent is not None:
+        if isinstance(self.parent, Pom):
             properties.update(self.parent.properties)
+        if isinstance(self.parent, Artifact):
             properties['parent.groupId'] = self.parent.group_id
             properties['parent.artifactId'] = self.parent.artifact_id
             properties['parent.version'] = str(self.parent.version)