Pylint false positive for Flask's "app.logger": E1101: Method 'logger' has no 'debug' member (no-member)

Use create_logger instead.

from flask import Flask
from flask.logging import create_logger

APP = Flask(__name__)
LOG = create_logger(APP)


@APP.route('/')
def say_hello():
    LOG.debug('A debug message')
    LOG.error('An error message')
    return 'hello'

A solution to prevent these false positives, via pylint plugins:

pylintplugins.py

import sys

from astroid import MANAGER, scoped_nodes, extract_node
from astroid.builder import AstroidBuilder


def register(_linter):
    pass


def transform(f):
    if f.name == 'logger':
        for prop in ['debug', 'info', 'warning', 'error', 'addHandler']:
            f.instance_attrs[prop] = extract_node('def {name}(arg): return'.format(name=prop))


MANAGER.register_transform(scoped_nodes.FunctionDef, transform)

This workaround prevents linting errors on app.logger.debug, app.logger.info, app.logger.warning, app.logger.error and app.logger.addHandler.

In order to be used, the pylintplugins.py file needs to be loaded using the --load-plugins command line option:

PYTHONPATH="." pylint -E app --load-plugins pylintplugins

or by including the following line in the pylintrc configuration file:

load-plugins=pylintplugins

Also note that if you are importing app via another python file (such as a view file when using Blueprints):

1. If you import app like this, you will get lint errors on app.logger.info:

   from myapp import app

2. If you import app like this, you won't get lint errors on app.logger.info:

   from flask import current_app as app

From the documentation:

Flask solves this issue with the application context. Rather than referring to an app directly, you use the the current_app proxy, which points to the application handling the current activity.

I don't have a good answer as to why, but it works for me using pylint==2.2.2 on python3.6.6. As always, your milage may vary.