Gremlin-Python

Warnings

• gotcha Always close the `DriverRemoteConnection`. Failing to do so can lead to 'Unclosed Client Session' errors and resource leaks, especially in long-running applications or when repeatedly creating connections. Use a `try...finally` block or a context manager if available (though a direct `close()` call is most common for `DriverRemoteConnection`).
  Fix: Call `connection.close()` on your `DriverRemoteConnection` instance when you are finished with it.
• gotcha Some Gremlin step names are Python reserved keywords (e.g., `in`, `and`, `as`, `from`, `is`, `not`, `or`, `set`). These steps must be suffixed with an underscore (`_`) in Gremlin-Python (e.g., `g.V().in_()`, `__.not_()`).
  Fix: Append an underscore (`_`) to any Gremlin step that clashes with a Python reserved keyword (e.g., `in_()`, `not_()`).
• gotcha Gremlin-Python traversals are lazy; they do not execute until a terminal step is called. Common terminal steps include `.next()`, `.toList()`, `.toSet()`, or `.iterate()`. Forgetting a terminal step means your traversal will not be sent to the server.
  Fix: Ensure every traversal chain ends with a terminal step like `.next()`, `.toList()`, `.toSet()`, or `.iterate()` to trigger execution.
• breaking The `has(key, traversal)` step was removed due to its confusing behavior where it checked if the traversal yielded *any* results, not if the property's value matched the traversal's condition. This is a breaking change.
  Fix: Rewrite queries using `has(key, P)` predicates or other suitable filtering steps to explicitly check property values.
• breaking The semantics of the `repeat()` step changed to consistently treat its child traversal with global semantics, affecting how traversers are handled across loop iterations.
  Fix: Review existing `repeat()` traversals and adjust logic if they relied on the previous hybrid local/global behavior. Test thoroughly.
• breaking The `limit(local)`, `range(local)`, and `tail(local)` steps now consistently return a collection (e.g., a list) when operating on an iterable, even if the result size is one. Previously, a single result would be 'unboxed' and returned directly.
  Fix: Update application code to always expect a collection (e.g., `list`) from these steps and handle single-item results by accessing the first element if needed (e.g., `result[0]`).
• breaking Apache TinkerPop 3.8.0 (and thus Gremlin-Python 3.8.0) requires Python 3.10 or newer. Support for earlier Python versions has been dropped. Additionally, Jython support was entirely removed, meaning native Python lambdas no longer execute in Gremlin Server; use Gremlin-Groovy for server-side lambdas.
  Fix: Upgrade Python environment to 3.10 or later. If server-side lambdas are necessary, rewrite them in Gremlin-Groovy.

Install

• pip install gremlinpython Install latest version

Imports

• DriverRemoteConnection

  from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection

• traversal

  from gremlin_python.process.anonymous_traversal import traversal

  While 'GraphTraversal' exists, `traversal()` for creating a GraphTraversalSource is typically imported from `anonymous_traversal`.
• __

  from gremlin_python.process.graph_traversal import __

  Used for anonymous traversals within other steps (e.g., `g.V().has('age', __.gt(20))`).
• statics.load_statics(globals())

  from gremlin_python import statics
  statics.load_statics(globals())

  Calling `statics.load_statics(globals())` allows direct use of many Gremlin steps (like `out()`, `in_()`) without the `__` prefix. Without it, you'd need `g.V().__.out().toList()`.

Quickstart

Connects to a local Gremlin Server (defaults to `ws://localhost:8182/gremlin`), executes a simple traversal to count vertices, adds a new vertex, and then queries its name. It properly handles connection closing.

import os
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
from gremlin_python.process.anonymous_traversal import traversal

GREMLIN_SERVER_URL = os.environ.get('GREMLIN_SERVER_URL', 'ws://localhost:8182/gremlin')

# Establish a remote connection to the Gremlin Server
connection = None
try:
    connection = DriverRemoteConnection(GREMLIN_SERVER_URL, 'g')
    g = traversal().withRemote(connection)

    # Example Traversal: Get the count of all vertices
    vertex_count = g.V().count().next()
    print(f"Number of vertices: {vertex_count}")

    # Add a vertex and then query it
    new_vertex = g.addV('person').property('name', 'Alice').next()
    print(f"Added vertex: {new_vertex.id} - {new_vertex.label}")

    alice_name = g.V(new_vertex.id).values('name').next()
    print(f"Name of added vertex: {alice_name}")

finally:
    # Ensure the connection is closed to release resources
    if connection:
        connection.close()