[Pytest-commit] Issue #518: parametrize: allow ellipsis to avoid repeating argument list? (hpk42/pytest)

[Matthias Geier]

New issue 518: parametrize: allow ellipsis to avoid repeating argument list?
https://bitbucket.org/hpk42/pytest/issue/518/parametrize-allow-ellipsis-to-avoid

Matthias Geier:

I'm new to py.test, so please forgive me if this is nonsense ...

I really like py.test and especially the parametrize-feature but I found it gets a bit tedious if I have many arguments in my test function.

The problem is that I basically have to repeat the whole list of arguments: I have to write them once in the string-argument to the `parametrize` decorator and then again in the argument list of the test function itself.

Here's an example:

```
#!python

import pytest

testparams = [
    (1, 2, 3, 4, 5, 6, 7, 8),
    (8, 7, 6, 5, 4, 3, 2, 1),
]

@pytest.mark.parametrize("a, b, c, d, e, f, g, h", testparams)
def test_many_args(a, b, c, d, e, f, g, h):
    assert False

```

I thought it would be nice if the decorator could automatically deduce the list of arguments from the test function, like this:


```
#!python

@pytest.mark.parametrize(..., testparams)
def test_many_args(a, b, c, d, e, f, g, h):
    assert False
```

In Python 2.x, you'd have to use `Ellipsis` instead of `...`, of course.

I tried to implement this and came up with a little patch:


```
#!diff

diff -r 95655acb1f90 _pytest/python.py
--- a/_pytest/python.py	Mon May 19 20:32:09 2014 +0200
+++ b/_pytest/python.py	Sat May 24 16:14:38 2014 +0200
@@ -796,7 +796,9 @@
             unwrapped_argvalues.append(argval)
         argvalues = unwrapped_argvalues
 
-        if not isinstance(argnames, (tuple, list)):
+        if argnames is Ellipsis:
+            argnames = inspect.getargspec(self.function)[0][:len(argval)]
+        elif not isinstance(argnames, (tuple, list)):
             argnames = [x.strip() for x in argnames.split(",") if x.strip()]
             if len(argnames) == 1:
                 argvalues = [(val,) for val in argvalues]
```

I'm sorry that I didn't make a pull request, but I have no clue about Mercurial.
But I guess the change is small enough.

Fixture arguments to the test function do still work, but now they have to be in the end of the argument list, e.g.:


```
#!python

@pytest.fixture
def myfixture():
    pass

@pytest.mark.parametrize(..., testparams)
def test_many_args_and_fixture(a, b, c, d, e, f, g, h, myfixture):
    assert False
```

What do you think of this idea?
Has something like this been discussed already?