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brain: Add __class_getitem__ to subprocess.Popen starting from Python 3.9 #882

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Jan 23, 2021
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brain: Add __class_getitem__ to subprocess.Popen starting from Python 3.9 #882

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4 changes: 4 additions & 0 deletions ChangeLog
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Expand Up @@ -7,6 +7,10 @@ What's New in astroid 2.5.0?
============================
Release Date: TBA

* Add ``__class_getitem__`` method to ``subprocess.Popen`` brain under Python 3.9 so that it is seen as subscriptable by pylint.

Fixes PyCQA/pylint#4034

* Adds `degrees`, `radians`, which are `numpy ufunc` functions, in the `numpy` brain. Adds `random` function in the `numpy.random` brain.

Fixes PyCQA/pylint#3856
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7 changes: 7 additions & 0 deletions astroid/brain/brain_subprocess.py
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Expand Up @@ -14,6 +14,7 @@
import astroid


PY39 = sys.version_info >= (3, 9)
PY37 = sys.version_info >= (3, 7)
PY36 = sys.version_info >= (3, 6)

Expand Down Expand Up @@ -147,6 +148,12 @@ def kill(self):
"py3_args": py3_args,
}
)
if PY39:
code += """
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Shouldn't we use textwrap.dedent here too?

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@hippo91 : I don't think we can. dedent() removes all common leading whitespaces, which means that calling this:

textwrap.dedent(
    """
    def __class_getitem__(cls, item):
        pass
    """
)

... returns this string:

def __class_getitem__(cls, item):
    pass

... which looks like a function, whereas we want the code to be indented to denote a method. Of course we could use textwrap.indent() too, like this:

textwrap.indent(
    textwrap.dedent(
        """
        def __class_getitem__(cls, item):
            pass
        """
    ),
    ' ' * 4,
)

but I am not sure it's more readable. :)

I thus prefer the current version. What do you think?

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@dbaty you are totally right!
Thanks for this explanation and this PR!

@classmethod
def __class_getitem__(cls, item):
pass
"""

init_lines = textwrap.dedent(init).splitlines()
indented_init = "\n".join(" " * 4 + line for line in init_lines)
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7 changes: 7 additions & 0 deletions tests/unittest_brain.py
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Expand Up @@ -1292,6 +1292,13 @@ def test_subprcess_check_output(self):
assert isinstance(inferred, astroid.Const)
assert isinstance(inferred.value, (str, bytes))

@test_utils.require_version("3.9")
def test_popen_does_not_have_class_getitem(self):
code = """import subprocess; subprocess.Popen"""
node = astroid.extract_node(code)
inferred = next(node.infer())
assert "__class_getitem__" in inferred


class TestIsinstanceInference:
"""Test isinstance builtin inference"""
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