Add support for lazy type annotations PEP563 (#112)

[ydylla]

Hi @yukinarit,
I added basic support for from __future__ import annotations.

Do you have any ideas how we could tell pytest to skip test_lazy_type_evaluation.py when using python 3.6 since the annotations future does not exist there?

Closes #112

[yukinarit]

Hi @ydylla
Thank you for the contribution!

Do you have any ideas how we could tell pytest to skip test_lazy_type_evaluation.py when using python 3.6 since the annotations future does not exist there?

Did you try pytest.mark.skipif? Sounds like this is what you are looking for.

import sys
@pytest.mark.skipif(sys.version_info < (3, 0),
                    reason="requires Python3")
def test_function():
    ...

https://docs.pytest.org/en/reorganize-docs/new-docs/user/skipping.html

[ydylla]

Yes I am aware of pytest.mark.skipif, sorry I should have mention that.
The Problem is that the python 3.6 tests fail at from __future__ import annotations which has to be the first line in a file.
I think we need a way to ignore the complete test_lazy_type_evaluation.py file in the pipeline. But I have not much experience with github wokflows. An ugly hack could be to just delete the file before starting pytest 😄

I also forgot to mention that I added tests for forward references with this.
We can not really support forward references, but maybe we should mention the workaround in the docs/readme. Which basically is call deserialize & serialize only after all classes that are used in the forward reference are visible globally.

@dataclass
class A:
  v: 'B'

@serialize
@deserialize
@dataclass
class B:
  v: int

# B is now visible so we can setup A
serialize(A)
deserialize(A)

[yukinarit]

@ydylla
Oh! Now I understand the problem!

I found a workaround in pydantic project. Could you check it is applicable to our case?

kip_pre_37 = pytest.mark.skipif(sys.version_info < (3, 7), reason='testing >= 3.7 behaviour only')


@skip_pre_37
def test_postponed_annotations(create_module):
    module = create_module(
        # language=Python
        """
from __future__ import annotations
from pydantic import BaseModel
class Model(BaseModel):
    a: int
"""
    )
    m = module.Model(a='123')
    assert m.dict() == {'a': 123}

https://github.com/samuelcolvin/pydantic/blob/master/tests/test_forward_ref.py#L8-L24

[yukinarit]

LGTM!

[codecov]

Codecov Report

Merging #126 (4f0abac) into master (f6a36ba) will decrease coverage by 0.14%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
- Coverage   89.28%   89.13%   -0.15%     
==========================================
  Files          11       11              
  Lines        1017     1031      +14     
  Branches      224      227       +3     
==========================================
+ Hits          908      919      +11     
- Misses         70       71       +1     
- Partials       39       41       +2     

Impacted Files	Coverage Δ
serde/compat.py	93.26% <94.44%> (-1.12%)	⬇️
serde/core.py	90.81% <100.00%> (-0.05%)	⬇️

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[ydylla]

Hi @yukinarit,
I tried to dynamically create modules like pydantic, but I could not get it to work properly.
Also I did not like that a lot of code only existed as string, which makes debugging very annoying.
Instead, I pushed a fix that just deletes the whole file for python 3.6.
Which was way easier and should probably be fine until 2021-12-23 when python 3.6 goes out of support anyways.

If you have no objections you can merge this.

[yukinarit]

@ydylla
I found another workaround which sounds like a good fit. What do you think?

Create conftest.py in the project root.

import sys

if sys.version_info[:2] == (3, 6):
    collect_ignore = ["tests/test_lazy_type_evaluation.py"]

For more information, please check: https://docs.pytest.org/en/6.2.x/example/pythoncollection.html#customizing-test-collection

[ydylla]

Thanks @yukinarit,
this is definitely better (the intended way to do this).

[yukinarit]

LGTM!

[yukinarit]

@ydylla
Thanks! Let me know if you need the latest pyserde on PyPI now.

[ydylla]

Currently, not necessarily. I already use it via git installation.