RecursionError: maximum recursion depth exceeded in Flask Pytest

Question

I am using Pytest to test a Flask + SQLAlchemy application. This is the content of tests/contftest.py

import pytest
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from flask import _app_ctx_stack
from flask.ext.sqlalchemy import SQLAlchemy, BaseQuery
from package.myapp import create_app
from package.config import DefaultConfig

DbSession = scoped_session(
        sessionmaker(),
        scopefunc=_app_ctx_stack.__ident_func__
    )
@pytest.fixture(scope='session')
def app(request):
    _app = create_app()
    _app.debug = False

    _app.engine = create_engine(_app.config['SQLALCHEMY_DATABASE_URI'], connect_args={"options": "-c timezone=utc"})
    global DbSession
    DbSession.configure(bind=_app.engine, query_cls=BaseQuery)

    # Establish an application context before running the tests.
    ctx = _app.app_context()
    ctx.push()

    @_app.teardown_appcontext
    def teardown(exception=None):
        ctx.pop()
        global DbSession
        if DbSession:
            DbSession.remove()


    request.addfinalizer(teardown)
    return _app

When I run pytest, I get this error message

___________________ ERROR at teardown of test_create_project ___________________

exception = None

    @_app.teardown_appcontext
    def teardown(exception=None):
>       ctx.pop()

tests/conftest.py:31: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../.virtualenvs/quest-backend/lib/python3.6/site-packages/flask/ctx.py:189: in pop
    self.app.do_teardown_appcontext(exc)
../../.virtualenvs/quest-backend/lib/python3.6/site-packages/flask/app.py:1892: in do_teardown_appcontext
    func(exc)
tests/conftest.py:31: in teardown
    ctx.pop()
E   RecursionError: maximum recursion depth exceeded
!!! Recursion detected (same locals & position)

Roman Kutlak · Accepted Answer · 2017-10-19 12:55:51Z

3

I don't think you are supposed to call ctx.pop() in your teardown function as the call to pop() invokes the registered teardown callbacks (hence the infinite recurAppContext calls Flask.do_teardown_appcontext() which contains the following:

for func in reversed(self.teardown_appcontext_funcs):
    func(exc)

You should call ctx.pop() when you are destroying your fixture.

answered Oct 19, 2017 at 12:55

Roman Kutlak

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MarSoft · Accepted Answer · 2017-10-19 14:59:59Z

Expanding Roman Kutlak's answer, here is how I would rewrite your app fixture:

@pytest.fixture(scope='session')
def app():
    _app = create_app()
    _app.debug = False

    _app.engine = create_engine(_app.config['SQLALCHEMY_DATABASE_URI'], connect_args={"options": "-c timezone=utc"})
    # session should probably not be global?..
    DbSession = scoped_session(
        sessionmaker(),
        scopefunc=_app_ctx_stack.__ident_func__
    )
    DbSession.configure(bind=_app.engine, query_cls=BaseQuery)

    # Establish an application context before running the tests.
    ctx = _app.app_context()
    ctx.push()

    # this function is specifically for app's teardown, don't call it again for fixture teardown
    @_app.teardown_appcontext
    def teardown(exception=None):
        if DbSession:
            DbSession.remove()

    # here is where tests will be executed
    yield _app

    # now tear-down our fixture (as apposed to flask app's teardown)
    ctx.pop()

It is not needed to use global keyword unless you want to assign a value to global variable from within inner scope.

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