Fix bugs where overriding init in a dataclass subclass crashed mypy #8159

beckjake · 2019-12-17T16:20:19Z

This fixes two bugs related to dataclass InitVars and overriding __init__
by changing mypy to ignore InitVars in parent classes when
the class supplied its own __init__ and set (init=False) on the dataclass.

It also fixes a bug with multiple inheritance of dataclasses.

Previously dataclasses attempted to look up the current class' __init__ to find
the definition of InitVars, which worked fine as long as the current class was
a direct subclass of the parent and didn't override __init__.

Unfortunately that didn't work when the InitVar came from a subclass that was
not first in MRO, or the parent had an item in its __init__ definition that
the subclass didn't use.

Now mypy will look up the __init__ for the current parent class that is being
processed in order to find the appropriate InitVar definition.

I've added test cases for all the issues.

This fixes two bugs related to dataclass InitVars and overriding __init__ (python#8022 and python#8015) by changing mypy to ignore InitVars in parent classes when the class supplied its own __init__ and set (init=False) on the dataclass. It also fixes a bug with multiple inheritance of dataclasses. Previously dataclasses attempted to look up the current class' __init__ to find the definition of InitVars, which worked fine as long as the current class was a direct subclass of the parent and didn't override __init__. Unfortunately that didn't work when the InitVar came from a subclass that was not first in MRO, or the parent had an item in its __init__ definition that the subclass didn't use. Now mypy will look up the __init__ for the current parent class that is being processed in order to find the appropriate InitVar.

ilevkivskyi

Thanks for PR, looks very good! I just have couple small suggestions about tests.

test-data/unit/check-dataclasses.test

In python#8159, I fixed InitVar handling so that it looked up the superclass __init__ and used that to determine the definition of InitVars. That fix doesn't work in the presence of `init=False` subclasses of the initial `init=False` class In that case, the lookup fails because the first attribute reached in MRO order on the subclass is the intermediate class, which also doesn't have the variable in its `__init__`. Then mypy didn't know about the InitVar but still tried to process it as if it did, resulting in an assertion error. This PR fixes that issue by not adding the field to the set of known attrs until an actual definition is found.

…8208) Fixes #8207 In #8159, I fixed InitVar handling so that it looked up the superclass __init__ and used that to determine the definition of InitVars. That fix doesn't work in the presence of `init=False` subclasses of the initial `init=False` class In that case, the lookup fails because the first attribute reached in MRO order on the subclass is the intermediate class, which also doesn't have the variable in its `__init__`. Then mypy didn't know about the InitVar but still tried to process it as if it did, resulting in an assertion error. This PR fixes that issue by not adding the field to the set of known attrs until an actual definition is found.

ilevkivskyi approved these changes Dec 19, 2019

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ilevkivskyi merged commit 387a911 into python:master Dec 19, 2019
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beckjake deleted the handle-initvar-overrides branch Dec 23, 2019

beckjake mentioned this pull request Dec 27, 2019

dataclass inheritance: deeply nested InitVar overrides crash mypy #8207

Closed

beckjake mentioned this pull request Dec 27, 2019

dataclasses: Fix deeply nested InitVar definitions with init=False #8208

Merged

Fix bugs where overriding init in a dataclass subclass crashed mypy #8159

Fix bugs where overriding init in a dataclass subclass crashed mypy #8159

beckjake commented Dec 17, 2019 •

edited by ilevkivskyi

ilevkivskyi left a comment

Fix bugs where overriding init in a dataclass subclass crashed mypy #8159

Fix bugs where overriding init in a dataclass subclass crashed mypy #8159

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beckjake commented Dec 17, 2019 • edited by ilevkivskyi

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beckjake commented Dec 17, 2019 •

edited by ilevkivskyi