pytest.mark.parametrize cannot locate argument name when there is another decorator

Created on 24 Feb 2020 · 6Comments · Source: pytest-dev/pytest

This is a feature request.

Description

When pytest.mark.parametrize is combined with another decorator that takes (*args, **kwargs), it can't find the correct argument name, see examples below.

Not working

import pytest

def mydeco(foo):
  def wrapped(*args, **kwargs):
    print('wrapped!')
    return foo(*args, **kwargs)

  return wrapped

@pytest.mark.parametrize('x', [1, 2, 3])
@mydeco
def test_func(x):
  assert x == 233

(opengl) [bate@archit taichi]$ pytest asas.py
============================================= test session starts =============================================
platform linux -- Python 3.8.1, pytest-5.3.4, py-1.8.1, pluggy-0.13.1
rootdir: /home/bate/Develop/taichi
plugins: xdist-1.31.0, forked-1.1.3
collected 0 items / 1 error                                                                                   

=================================================== ERRORS ====================================================
__________________________________________ ERROR collecting asas.py ___________________________________________
In wrapped: function uses no argument 'x'
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
============================================== 1 error in 0.06s ===============================================



md5-60f0c816de5df709266c88e9b49f6f6f

(opengl) [bate@archit taichi]$ pytest asas.py
============================================= test session starts =============================================
platform linux -- Python 3.8.1, pytest-5.3.4, py-1.8.1, pluggy-0.13.1
rootdir: /home/bate/Develop/taichi
plugins: xdist-1.31.0, forked-1.1.3
collected 3 items

asas.py FFF [100%]

================================================== FAILURES ===================================================
________________________________________________ test_func[1] _________________________________________________

x = 1

@pytest.mark.parametrize('x', [1, 2, 3])
def test_func(x):

assert x == 233
E assert 1 == 233

asas.py:5: AssertionError
________________________________________________ test_func[2] _________________________________________________

x = 2

@pytest.mark.parametrize('x', [1, 2, 3])
def test_func(x):

assert x == 233
E assert 2 == 233

asas.py:5: AssertionError
________________________________________________ test_func[3] _________________________________________________

x = 3

@pytest.mark.parametrize('x', [1, 2, 3])
def test_func(x):

assert x == 233
E assert 3 == 233

asas.py:5: AssertionError
============================================== 3 failed in 0.03s ==============================================


## Why we need this?
@k-ye was trying to apply a test for all architectures using our `@ti.all_archs` decorator. It must be the last decorator to function so that `ti.init()` could be called for each test.
Then, we want to use `parametrize` and failed due to the reason shown above.
Discussion: https://github.com/taichi-dev/taichi/pull/527#issuecomment-590261599

## Possible solutions:
Thanks to @k-ye:
```py
def parametrize(argnames: str, argvalues):
  # @pytest.mark.parametrize only works for canonical function args, and doesn't
  # support *args or **kwargs. This makes it difficult to play along with other
  # decorators like @ti.all_archs. As a result, we implement our own.
  argnames = [s.strip() for s in argnames.split(',')]
  def iterable(x):
    try:
      _ = iter(x)
      return True
    except:
      return False

  def decorator(test):
    def wrapped(*test_args, **test_kwargs):
      for vals in argvalues:
        if isinstance(vals, str) or not iterable(vals):
          vals = (vals, )
        kwargs = {k: v for k, v in zip(argnames, vals)}
        assert len(kwargs.keys() & test_kwargs.keys()) == 0
        kwargs.update(test_kwargs)
        test(*test_args, **kwargs)
    return wrapped
  return decorator

parametrize question

Source

archibate

Most helpful comment

It works correctly if your decorator is well-behaved and uses functools.wraps:

import functools

import pytest

def mydeco(foo):
  @functools.wraps(foo)
  def wrapped(*args, **kwargs):
    print('wrapped!')
    return foo(*args, **kwargs)

  return wrapped

@pytest.mark.parametrize('x', [1, 2, 3])
@mydeco
def test_func(x):
  assert x == 233

I don't think this is something pytest should work around.

The-Compiler on 24 Feb 2020

👍2

All 6 comments

It works correctly if your decorator is well-behaved and uses functools.wraps:

import functools

import pytest

def mydeco(foo):
  @functools.wraps(foo)
  def wrapped(*args, **kwargs):
    print('wrapped!')
    return foo(*args, **kwargs)

  return wrapped

@pytest.mark.parametrize('x', [1, 2, 3])
@mydeco
def test_func(x):
  assert x == 233

I don't think this is something pytest should work around.

The-Compiler on 24 Feb 2020

👍2

Thank you! It was really my problem not using decoration correctly...

archibate on 24 Feb 2020

Thanks! I wonder if this is documented somewhere, or is @functools.wraps a known trick to preserve the function signature info? A quick search on Stackoverflow and I found the closest answer to be using @decorator.decorator: https://stackoverflow.com/a/12200860/12003165