How to add an edge to existing and new vertices in gremlin-python? - gremlin

Question

I've already seen this answer:
Gremlin, How to add edge to existing vertex in gremlin-python
and it wasn't really helpful. As suggested in one of the comments I did try to update gremlinpython 3.3.0 but then I get key error.
Stack:
JanusGraph 0.2.0, gremlinpython3.2.3
This is my code
from gremlin_python import statics
from gremlin_python.structure.graph import Graph
from gremlin_python.process.graph_traversal import __
from gremlin_python.process.strategies import *
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
graph = Graph()
g = graph.traversal().withRemote(DriverRemoteConnection('ws://localhost:8182/gremlin','g'))
martha = g.V().has('name','martha').next()
jack = g.V().has('name','jack').next()
#e_id = g.addE(jack,'likes',martha).next()
e_id = g.V(martha).as_('to').V(jack).addE("Likes").to('to').toList()
print e_id.toList()
StackTrace with gremlinpython 3.3.0
Traceback (most recent call last):
File "gremlin-py.py", line 9, in <module>
martha = g.V().has('name','martha').next()
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 70,in next
return self.__next__()
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 43,in __next__
self.traversal_strategies.apply_strategies(self)
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 352, in apply_strategies
traversal_strategy.apply(traversal)
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/driver/remote_connection.py", line 143, in apply
remote_traversal = self.remote_connection.submit(traversal.bytecode)
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/driver/driver_remote_connection.py", line 54, in submit
results = result_set.all().result()
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/concurrent/futures/_base.py", line 429, in result
return self.__get_result()
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/concurrent/futures/_base.py", line 381, in __get_result
raise exception_type, self._exception, self._traceback
KeyError: None
In my case, 3.3.0 is throwing error for all queries including g.V().next(). Now going back to 3.2.3, addvertex and other queries are working absolutely fine, but I couldn't figure out how to add edges. The same code when run with 3.2.3 produces,
StackTrace with gremlinpython 3.2.3
Traceback (most recent call last): File "gremlin-py.py", line 12, in <module>
e_id = g.V(martha).as_('to').V(jack).addE("Likes").to('to').toList()
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 52, in toList return list(iter(self))
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 70, in next
return self.__next__() File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 43, in __next__
self.traversal_strategies.apply_strategies(self) File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/process/traversal.py", line 284, in apply_strategies
traversal_strategy.apply(traversal)
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/driver/remote_connection.py", line 95, in apply remote_traversal = self.remote_connection.submit(traversal.bytecode) File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/driver/driver_remote_connection.py", line 53, in submit traversers = self._loop.run_sync(lambda: self.submit_traversal_bytecode(request_id, bytecode))
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/tornado/ioloop.py", line 457, in run_sync
return future_cell[0].result() File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/tornado/concurrent.py", line 237, in result
raise_exc_info(self._exc_info)
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/tornado/gen.py", line 285, in wrapper
yielded = next(result)
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/driver/driver_remote_connection.py", line 69, in submit_traversal_bytecode
"gremlin": self._graphson_writer.writeObject(bytecode),
File "/Users/arvindn/.virtualenvs/gremlinenv/lib/python2.7/site-packages/gremlin_python/structure/io/graphson.py", line 72, in writeObject
return json.dumps(self.toDict(objectData), separators=(',', ':'))
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 250, in dumps
sort_keys=sort_keys, **kw).encode(obj)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/encoder.py", line 207, in encode
chunks = self.iterencode(o, _one_shot=True)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/encoder.py", line 270, in iterencode
return _iterencode(o, 0)
File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/encoder.py", line 184, in default
raise TypeError(repr(o) + " is not JSON serializable")
TypeError: v[4184] is not JSON serializable
It says v[x] is not JSON serializable. I'm not sure what causes this error. It'll be awesome if someone can help. If any more info is needed, I shall update the question accordingly.

Answer 1

JanusGraph 0.2.0 uses Apache TinkerPop 3.2.6. You should use the 3.2.6 version of the gremlinpython driver.
pip uninstall gremlinpython
pip install gremlinpython==3.2.6