Connecting from Python

Gremlin traversals can be constructed with Gremlin-Python just like in Gremlin-Java or Gremlin-Groovy. Refer to Gremlin Query Language for an introduction to Gremlin and pointers to further resources.

Important

Some Gremlin step and predicate names are reserved words in Python. Those names are simply postfixed with _ in Gremlin-Python, e.g., in() becomes in_(), not() becomes not_(), and so on. The other names affected by this are: all, and, as, from, global, is, list, or, and set.

Getting Started with JanusGraph and Gremlin-Python

To get started with Gremlin-Python:

Install Gremlin-Python:
```
pip install gremlinpython==3.7.3
```

Create a text file gremlinexample.py and add the following imports to it:

from gremlin_python import statics
from gremlin_python.structure.graph import Graph
from gremlin_python.process.graph_traversal import __
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection

Create a GraphTraversalSource which is the basis for all Gremlin traversals:

from gremlin_python.process.anonymous_traversal import traversal

connection = DriverRemoteConnection('ws://localhost:8182/gremlin', 'g')
# The connection should be closed on shut down to close open connections with connection.close()
g = traversal().withRemote(connection)
# Reuse 'g' across the application

Execute a simple traversal:
```
hercules_age = g.V().has('name', 'hercules').values('age').next()
print(f'Hercules is {hercules_age} years old.')
```
next() is a terminal step that submits the traversal to the Gremlin Server and returns a single result.

JanusGraph-Python for JanusGraph Specific Types and Predicates

JanusGraph contains some types and predicates that are not part of Apache TinkerPop and are therefore also not supported by Gremlin-Python. JanusGraph-Python is a Python package that adds support for some of these types and predicates to Gremlin-Python.

After installing the package, a message serializer needs to be configured for JanusGraph which can be done like this for GraphSON 3:

from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
from janusgraph_python.driver.serializer import JanusGraphSONSerializersV3d0

connection = DriverRemoteConnection(
  'ws://localhost:8182/gremlin', 'g',
  message_serializer=JanusGraphSONSerializersV3d0())

or like this for GraphBinary:

from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
from janusgraph_python.driver.serializer import JanusGraphBinarySerializersV1

connection = DriverRemoteConnection(
  'ws://localhost:8182/gremlin', 'g',
  message_serializer=JanusGraphBinarySerializersV1())

Refer to the documentation of JanusGraph-Python for more information about the package, including its compatibility with different JanusGraph versions and differences in support between the different serialization formats.