Understanding "Too many ancestors" from pylint

Question

example.py:

'''
demo too many ancestors 
'''
from flask_security.forms import RegisterForm
from wtforms.fields import TextField

class ExtendedRegisterForm(RegisterForm):
    '''An extended register form'''
    name = TextField('Name', [])

When I run pylint:

$ pylint -r n example.py
************* Module example
R:  7, 0: Too many ancestors (10/7) (too-many-ancestors)

What does this mean and how can I fix it?

Answer 1

The problem is that you inherit from a class which has itself (too) many ancestors: RegisterForm. In your case, you can't do a lot about this, beside stopping using it which is probably not an option. So you may want to disable this message for this class, eg:

class ExtendedRegisterForm(RegisterForm): # pylint: disable=too-many-ancestors

Answer 2

In addition to the disabling directives in the source code, you can configure this through the --max-parents= commandline option. You can also specify this in the config file (.pylintrc):

[DESIGN]
max-parents=15

As you can see I set it to 15 as many classes in Django (my project), particularly its view classes, will have hierarchies that are deeper than the default 7.

Answer 3

From documentation here: https://pylint.readthedocs.io/en/stable/technical_reference/features.html

too-many-ancestors (R0901): Too many ancestors (%s/%s) Used when class has too many parent classes, try to reduce this to get a simpler (and so easier to use) class.

Answer 4

basically Add to json or .pylintrc --max-parents='yourrequirednumber'

Note: --max-parents=7 is default

If using Visual Studio Code (VSC) you can easily override default config with adding below code to settings.json

Go to --> UserSettings ctrl+, (default shortcut) --> click ... (more actions) --> open settings.json --> Add to overwrite Default settings this code:

"python.linting.pydocstyleArgs": ["--max-parents=25"]

NOTE2: if pylint_django is not installed: $ pip install pylint-django