shaare.it

NameError: name 'g' is not defined

7 Dec 2025

1 min read

python flask errors

NameError: name ‘g’ is not defined

$ python - <<'PY'
from flask import Flask
app = Flask(__name__)
print(g)
PY
Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
NameError: name 'g' is not defined

Why this happens

g is provided by Flask as a context-local proxy stored in flask.g. If you reference g without importing it or outside an application/request context, you’ll get NameError or RuntimeError. It’s common when moving code into standalone modules or CLI scripts.

Fix

  • Import g explicitly: from flask import g.
  • Use with app.app_context(): for application-level data; use request handlers for request data.
  • Don’t access g at import-time; use it inside functions after context is pushed.

Wrong code

from flask import Flask
app = Flask(__name__)

# Global scope access
g.user_id = 1

Fixed code

from flask import g

def set_user():
    g.user_id = 1

Context example:

from flask import Flask, g
app = Flask(__name__)

with app.app_context():
    g.x = 10
    assert g.x == 10

Remember: g is per-request/per-context. Import it and use it only when a context is active.