Assignment Expressions

[da-dada]

if (init := getattr(inst, 'init', None)) and callable(init): gives E0601 Using variable 'init' before assignment and E1102 'init' is not callable ('inst' is a given instance and 'init' a method of it)

[dbaty]

Here is a reformatted snippet:

# pylint: disable=missing-module-docstring, missing-class-docstring, missing-function-docstring
# pylint: disable=too-few-public-methods
# pylint: disable=invalid-name

class C:
    def init(self):
        pass

c = C()
if init := getattr(c, 'init', None) and callable(init):
    pass

pylint says:

test.py:10:49: E0601: Using variable 'init' before assignment (used-before-assignment)

In fact, Python 3.8 fails with a NameError:

$ python ~/test.py
Traceback (most recent call last):
  File "test.py", line 10, in <module>
    if init := getattr(c, 'init', None) and init():
NameError: name 'init' is not defined 

So I don't think that pylint output is wrong. I am not yet too familiar with the walrus operator, so I may be missing something. Perhaps this syntax works as of Python 3.9?

As for the E1102 warning (not-callable) that you report, you'll need to provide further details. Your snippet does not call init, so I don't see how pylint could report not-callable (and, as show above, it clearly doesn't). Also, note that pylint sometimes cannot guess if attributes fetched through getattr are of a particular type. This may be your issue on your real code (not the snippet you provided).

[da-dada]

Python 3.8 works fine and I know that a static linter can’t check all dynamic features the Assignment Expressions is described in PEP 572 and what you seem to miss is ‘The := operator groups more tightly than a comma in all syntactic positions where it is legal, but less tightly than all other operators’ I gave the example ‘if (init := getattr(inst, 'init', None)) and callable(init):’ and accordingly the brackets are of substance!!!!!!!!!!! the E1102 is a sequel and you may safely forget about it I’m very pleased with pylint and I just like to help improving it From: Damien Baty Sent: Monday, September 28, 2020 5:00 PM To: PyCQA/pylint Cc: da-dada ; Author Subject: Re: [PyCQA/pylint] Assignment Expressions (#3865) Here is a reformatted snippet: # pylint: disable=missing-module-docstring, missing-class-docstring, missing-function-docstring # pylint: disable=too-few-public-methods # pylint: disable=invalid-name class C: def init(self): pass c = C() if init := getattr(c, 'init', None) and callable(init): passpylint says: test.py:10:49: E0601: Using variable 'init' before assignment (used-before-assignment) In fact, Python 3.8 fails with a NameError: $ python ~/test.py Traceback (most recent call last): File "test.py", line 10, in <module> if init := getattr(c, 'init', None) and init(): NameError: name 'init' is not defined So I don't think that pylint output is wrong. I am not yet too familiar with the walrus operator, so I may be missing something. Perhaps this syntax works as of Python 3.9? As for the E1102 warning (not-callable) that you report, you'll need to provide further details. Your snippet does not call init, so I don't see how pylint could report not-callable (and, as show above, it clearly doesn't). Also, note that pylint sometimes cannot guess if attributes fetched through getattr are of a particular type. This may be your issue on your real code (not the snippet you provided). — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[dbaty]

Indeed, I forgot the parentheses. A reproducible snippet is hence:

# pylint: disable=missing-module-docstring

if (a := lambda: 2) and a():
    print("ok")

pylint output (master branch, as of 2020-09-29):

test.py:3:24: E0601: Using variable 'a' before assignment (used-before-assignment)

pylint is indeed wrong, here.

[hippo91]

@dbaty thanks for the snippet. Thanks to it i can reproduce the bug.