TypeError exception when method named "format" replaces itself with different method

[BlankSpruce]

Steps to reproduce

1. Create a file with following class in either of these two variants:

class Foo:
    def _format(self):
        pass

    def format(self):
        self.format = self._format
        self.format()

or

class Foo:
    def _format(self):
        pass

    def format(self):
        self.format = self._format
        self._format()

2. Run pylint on such file.

Current behavior

$ pylint reproduce.py
************* Module reproduce
reproduce.py:1:0: C0114: Missing module docstring (missing-module-docstring)
reproduce.py:1:0: C0115: Missing class docstring (missing-class-docstring)
reproduce.py:2:4: R0201: Method could be a function (no-self-use)
reproduce.py:5:4: C0116: Missing function or method docstring (missing-function-docstring)
Traceback (most recent call last):
  File "/home/foobar/.local/bin/pylint", line 8, in <module>
    sys.exit(run_pylint())
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/__init__.py", line 22, in run_pylint
    PylintRun(sys.argv[1:])
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/lint/run.py", line 344, in __init__
    linter.check(args)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/lint/pylinter.py", line 870, in check
    self._check_files(
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/lint/pylinter.py", line 904, in _check_files
    self._check_file(get_ast, check_astroid_module, name, filepath, modname)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/lint/pylinter.py", line 930, in _check_file
    check_astroid_module(ast_node)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/lint/pylinter.py", line 1062, in check_astroid_module
    retval = self._check_astroid_module(
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/lint/pylinter.py", line 1107, in _check_astroid_module
    walker.walk(ast_node)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/utils/ast_walker.py", line 75, in walk
    self.walk(child)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/utils/ast_walker.py", line 75, in walk
    self.walk(child)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/utils/ast_walker.py", line 72, in walk
    callback(astroid)
  File "/home/foobar/.local/lib/python3.8/site-packages/pylint/checkers/classes.py", line 992, in visit_functiondef
    for obj in ancestor.lookup(node.name)[1]:
  File "/home/foobar/.local/lib/python3.8/site-packages/astroid/node_classes.py", line 1067, in lookup
    return self.scope().scope_lookup(self, name)
  File "/home/foobar/.local/lib/python3.8/site-packages/astroid/scoped_nodes.py", line 2239, in scope_lookup
    return frame._scope_lookup(node, name, offset)
  File "/home/foobar/.local/lib/python3.8/site-packages/astroid/scoped_nodes.py", line 209, in _scope_lookup
    return pscope.scope_lookup(node, name)
  File "/home/foobar/.local/lib/python3.8/site-packages/astroid/scoped_nodes.py", line 514, in scope_lookup
    return self._scope_lookup(node, name, offset)
  File "/home/foobar/.local/lib/python3.8/site-packages/astroid/scoped_nodes.py", line 198, in _scope_lookup
    stmts = node._filter_stmts(self.locals[name], self, offset)
  File "/home/foobar/.local/lib/python3.8/site-packages/astroid/node_classes.py", line 1155, in _filter_stmts
    if stmt.fromlineno > mylineno > 0:
TypeError: '>' not supported between instances of 'NoneType' and 'int'

Expected behavior

$ pylint reproduce.py
************* Module reproduce
reproduce.py:1:0: C0114: Missing module docstring (missing-module-docstring)
reproduce.py:1:0: C0115: Missing class docstring (missing-class-docstring)
reproduce.py:5:4: C0116: Missing function or method docstring (missing-function-docstring)
reproduce.py:5:4: E0202: An attribute defined in reproduce line 6 hides this method (method-hidden)
reproduce.py:1:0: R0903: Too few public methods (1/2) (too-few-public-methods)

----------------------------------------------------------------------
Your code has been rated at -11.67/10 (previous run: -11.67/10, +0.00)

Additional info

The issue isn't reproduced if replaced method has different name:

class Foo:
    def _format(self):
        pass

    def definitely_not_a_format(self):
        self.definitely_not_a_format = self._format
        self.definitely_not_a_format()

or it doesn't replace itself:

class Foo:
    def _format(self):
        pass

    def format(self):
        self._format()

pylint --version output

pylint 2.5.3
astroid 2.4.0
Python 3.8.3 (default, May 17 2020, 18:15:42)
[GCC 10.1.0]

[bhack]

Do we need to update the minimal astroid version in https://github.com/PyCQA/pylint/blob/master/DEPENDS (and in debian control)?

[hippo91]

@PCManticore what do you think about it?

[PCManticore]

@hippo91 and @bhack Let's do it. Those are really old versions.

[bhack]

We Need a new astroid release

[bhack]

Check pylint-dev/astroid#886

[hippo91]

@bhack the new astroid version (1.5) has been released.

[bhack]

@hippo91 The minimal required version is still astroid 1.3.6 https://github.com/PyCQA/pylint/blob/master/DEPENDS

[hippo91]

@bhack sorry for the delay. I'm not aware of this kind of DEPENDS file. Can you explain me what is its purpose please?

[bhack]

Probably it is only for the MANIFEST https://github.com/PyCQA/pylint/blob/master/MANIFEST.in

[hippo91]

@bhack i have no idea of the possible use of the DEPENDS file. It has been added 15 years ago and i don't know if we still need it. @PCManticore @AWhetter @Pierre-Sassoulas @cdce8p have you any idea about this?

[Pierre-Sassoulas]

I think we're going to need to dust up the packaging at some point, we still have a compatibility with distutils in the setup.py who was replaced by setuptools a decade ago, and it seems there are also outdated confusing files all over the place. Right now the astroid dependencie version is defined in https://github.com/PyCQA/pylint/blob/master/pylint/__pkginfo__.py#L42. How about a clean new issue for moving to poetry/pyproject.toml and removing all this?

[bhack]

We have also Astroid version for Debian package in https://github.com/PyCQA/pylint/blob/master/debian/control#L22

[cdce8p]

@sandrotosi Maybe you can help here. What files are needed for including pylint in debian?
Most of the files in pylint/debian haven't been updated in over a decade. Are they even necessary or can they be removed entirely?

[sandrotosi]

not sure what you mean by "including pylint in debian". if it's having pylint available via debian repositories, then that's done via this repo https://salsa.debian.org/python-team/packages/pylint where (tbh) i completely disregard the debian/ directory provided upstream (that debianization is released under the same license of pylint, so feel free to use it accordingly).

if you mean creating a debian package once closinig PyCQA/pylint, then that's a bit more complicated, and as someone else already pointed out, the content of debian/ has not been kept up-to-date with debian packaging standards, and may need a serious revamp, but at that point i'd ask if it's really worth to keep it around at all (a question you guys should answer :) )

[AWhetter]

I'm all for moving to poetry and pyproject.toml.
If debian aren't using the files from the debian folder (which @sandrotosi has confirmed) then let's remove those.

[Pierre-Sassoulas]

Just opened #4193 to follow through.