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Merged
ericvsmith merged 7 commits into from
Jun 3, 2019
Merged

bpo-33569 Preserve type information with InitVar #8927

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e12ee98
Preserve type information with InitVar
hackaugusto Aug 25, 2018
7278da5
fix dataclassses tests
hackaugusto Aug 28, 2018
4116696
added news blurb
hackaugusto Aug 28, 2018
dbefb2c
dataclass: Added InitVar repr
hackaugusto Sep 15, 2018
e9c983f
added test for initvar type
hackaugusto Oct 7, 2018
c5cba2b
Merge remote-tracking branch 'upstream/master' into pr_8927
ericvsmith Jun 3, 2019
e73c331
Add a test for InitVar repr.
ericvsmith Jun 3, 2019
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13 changes: 10 additions & 3 deletions Lib/dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -201,10 +201,16 @@ def __repr__(self):

class _InitVarMeta(type):
def __getitem__(self, params):
return self
return InitVar(params)

class InitVar(metaclass=_InitVarMeta):
pass
__slots__ = ('type', )

@ericvsmith ericvsmith Sep 10, 2018

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We should probably have a nicer __repr__ here.

Currently you get:

>>> from dataclasses import InitVar
>>> InitVar[int]
<dataclasses.InitVar object at 0x00A041C0>

I'd suggest something like:

    def __repr__(self):
        return f'dataclasses.InitVar[{self.type}]'

for starters, although typing.ClassVar does something more sophisticated in place of {self.type}. Maybe someday when we import typing from dataclasses we can switch to using their helper function. It's probably worth adding a comment to that effect, too.

@hackaugusto hackaugusto Sep 15, 2018 •
edited
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Using f'dataclasses.InitVar[{self.type}]' would look like:

>>> from dataclasses import InitVar
>>> InitVar[int]
dataclasses.InitVar[<class 'int'>]

So I added f'dataclasses.InitVar[{self.type.__name__}]' instead. Should I write a test for this?

@ericvsmith ericvsmith Sep 15, 2018

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If that's what gives you the equivalent of:

>>> import typing
>>> typing.ClassVar[int]
typing.ClassVar[int]

Then I'm all for it.

Yes, we'll need tests for this. Nothing complex, InitVar[int] should be good enough.

@hackaugusto hackaugusto Oct 7, 2018 •
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Sorry for the delay, I added a really simple test:

self.assertEqual(InitVar[int].type, int)

Would you like tests using __repr__ and @dataclass?

@ericvsmith ericvsmith May 24, 2019

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I apologize for taking forever to get back to you on this.

Could you test the repr of an InitVar? Something like (untested) repr(InitVar[int]) == 'dataclasses.InitVar[int]'?

I promise I'll commit this as soon as you add this change.


def __init__(self, type):
self.type = type

def __repr__(self):
return f'dataclasses.InitVar[{self.type.__name__}]'


# Instances of Field are only ever created from within this module,
Expand Down Expand Up @@ -586,7 +592,8 @@ def _is_classvar(a_type, typing):
def _is_initvar(a_type, dataclasses):
# The module we're checking against is the module we're
# currently in (dataclasses.py).
return a_type is dataclasses.InitVar
return (a_type is dataclasses.InitVar
or type(a_type) is dataclasses.InitVar)


def _is_type(annotation, cls, a_module, a_type, is_type_predicate):
Expand Down
6 changes: 6 additions & 0 deletions Lib/test/test_dataclasses.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1097,6 +1097,12 @@ def __post_init__(self, init_param):
c = C(init_param=10)
self.assertEqual(c.x, 20)

def test_init_var_preserve_type(self):
self.assertEqual(InitVar[int].type, int)

# Make sure the repr is correct.
self.assertEqual(repr(InitVar[int]), 'dataclasses.InitVar[int]')

def test_init_var_inheritance(self):
# Note that this deliberately tests that a dataclass need not
# have a __post_init__ function if it has an InitVar field.
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-08-28-03-00-12.bpo-33569.45YlGG.rst
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@@ -0,0 +1 @@
dataclasses.InitVar: Exposes the type used to create the init var.