not-callable reported when calling a callable returned by non-trivial property

[jendagroovy]

Steps to reproduce

class ClsA(object):
    pass


class ClsB(object):

    def __init__(self):
        self._some_cls = None

    @property
    def some_cls(self):
        if self._some_cls:
            return self._some_cls

        self._some_cls = ClsA
        return ClsA

    def get_object(self):
        return self.some_cls()

Current behavior

pylint -E /tmp/x.py
************* Module x
E: 19,15: self.some_cls is not callable (not-callable)

Expected behavior

pylint -E /tmp/x.py

No output as the property actually returns a callable. Error should only be reported when there is a certainty, that the property can't return a callable.

pylint --version output

pylint 1.7.4,
astroid 1.5.3
Python 2.7.10 (default, Feb  7 2017, 00:08:15)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)]

[acatton]

Here's a real life example, with type annotations:

import bz2
import enum
import gzip
import typing


class Algo(enum.Enum):
    BZIP = 'bzip'
    GZIP = 'gzip'

    @property
    def compress(self) -> typing.Callable[[bytes], bytes]:
        return {
            Algo.BZIP: bz2.compress,
            Algo.GZIP: gzip.compress,
        }[self]


def compress(algo: str, data: bytes) -> bytes:
    return Algo(algo).compress(data)

$ mypy x.py
<nothing>
$ pylint x.py
No config file found, using default configuration
************* Module x
[…]
E: 20,11: Algo(algo).compress is not callable (not-callable)
[…]

[heyakyra]

Just came across this as well, and managed to find one SO question on it: https://stackoverflow.com/questions/53598374/pylint-giving-not-callable-error-for-object-property-that-is-callable

Also, is it expected that even without using @property instance variables are not callable?

Could this be related to #1493 ?

[PCManticore]

@acatton I can no longer reproduce the bug you were having using the latest not released yet version.

@heyakyra Do you have a reproduction case for which you get this error? The reason this wasn't inferrable for the original poster was the fact that pylint does not proper support for control flow understanding, which is why it had an issue with get_object and self.some_class but other than that pylint should be able to infer a callable coming from a property. An example would be great.

[heyakyra]

Seems to be caused by using a NamedTuple in particular in this case.

from typing import NamedTuple


class Test:
    def __init__(self, field):
        self.Item = NamedTuple("x", [(field, str)])
        self.item: self.Item

    def set_item(self, item):
        self.item = self.Item(item)

^ self.Item is not callable

[DanielNoord]

Seems to be caused by using a NamedTuple in particular in this case.

class Test:
    def __init__(self, field):
        self.Item = NamedTuple("x", [(field, str)])
        self.item: self.Item

    def set_item(self, item):
        self.item = self.Item(item)

^ self.Item is not callable

Should be fixed with #5537.

This leaves only the original post in this issue open. This is more difficult thought as we infer _some_cls to potentially be None. That requires some form of control flow inference.

[Pierre-Sassoulas]

Closing as it's been fixed in 2.15.0-dev0 or I can't reproduce it.

[jendagroovy]

Yeah, I can confirm that, actually looks like to have been fixed in 2.13.5 👍