Add __.V() wrapping for Vertex objects in to() and from() methods

- Wrap Vertex objects with __.V(vertex.id) in to() and from() steps
- Use isinstance() check to only wrap actual Vertex objects
- Revert __.V() wrapping for basic gremlin python examples
- Update integration tests to match and test new behavior

Author: kirill-stepanishin

CHANGELOG.asciidoc

@@ -82,6 +82,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 * Added `idleConnectionTimeout` setting for Gremlin Driver and automatic closing of idle connections
 * Enabled TCP Keep-Alive in GremlinServer.
 * Updated Python GLV examples to use HTTP and to run as part of the integration tests.
+* Fixed `gremlin-python` `to()` and `from_()` methods to wrap Vertex objects with `__.V()` for proper edge creation.
 
 == TinkerPop 3.8.0 (Grix Greven)
 

gremlin-python/src/main/python/examples/basic_gremlin.py

@@ -40,8 +40,8 @@ def main():
 
     # be sure to use a terminating step like next() or iterate() so that the traversal "executes"
     # iterate() does not return any data and is used to just generate side-effects (i.e. write data to the database)
-    g.V(v1).add_e('knows').to(__.V(v2)).property('weight', 0.75).iterate()
-    g.V(v1).add_e('knows').to(__.V(v3)).property('weight', 0.75).iterate()
+    g.V(v1).add_e('knows').to(v2).property('weight', 0.75).iterate()
+    g.V(v1).add_e('knows').to(v3).property('weight', 0.75).iterate()
 
     # retrieve the data from the "marko" vertex
     marko = g.V().has(VERTEX_LABEL, 'name', 'marko').values('name').next()

gremlin-python/src/main/python/gremlin_python/process/graph_traversal.py

@@ -28,6 +28,7 @@
 from ..driver.remote_connection import RemoteStrategy
 from .. import statics
 from ..statics import long
+from ..structure.graph import Vertex
 
 log = logging.getLogger("gremlinpython")
 
@@ -506,7 +507,10 @@ def format_(self, *args):
         return self
 
     def from_(self, *args):
-        self.gremlin_lang.add_step("from", *args)
+        if len(args) == 1 and isinstance(args[0], Vertex):
+            self.gremlin_lang.add_step("from", __.V(args[0].id))
+        else:
+            self.gremlin_lang.add_step("from", *args)
         return self
 
     def group(self, *args):
@@ -943,7 +947,10 @@ def times(self, *args):
         return self
 
     def to(self, *args):
-        self.gremlin_lang.add_step("to", *args)
+        if len(args) == 1 and isinstance(args[0], Vertex):
+            self.gremlin_lang.add_step("to", __.V(args[0].id))
+        else:
+            self.gremlin_lang.add_step("to", *args)
         return self
 
     def toE(self, *args):

gremlin-python/src/main/python/tests/process/test_traversal.py

@@ -370,7 +370,7 @@ def test_should_extract_id_from_vertex(self):
 
         # Test edge creation with from/to vertices
         from_to = g.add_e("Edge").from_(Vertex(1)).to(Vertex(2))
-        assert "g.addE('Edge').from(1).to(2)" == from_to.gremlin_lang.get_gremlin()
+        assert "g.addE('Edge').from(__.V(1)).to(__.V(2))" == from_to.gremlin_lang.get_gremlin()
 
         # Test mergeE() with Vertex in dictionary
         merge_map = {