[TIP] both naming a parameter and showing its values

[dpb dpb]

The way the ids parameter of parametrize currently works, we have the
choice either to show the actual argument values, one by one, or else a
string assigned to parameters as a whole:

import pytest
>
> @pytest.mark.parametrize('a', range(3))
> def test_funcs_without_name(a):
>     assert a ** 3 == a * (a ** 2)


> @pytest.mark.parametrize('a', range(3), ids=['value of a'] * 3)
> def test_funcs_with_name(a):
>     assert a ** 3 == a * (a ** 2)
>
> $ py.test params/demo_ids.py -v
> ============================= test session starts
> ==============================
> platform darwin -- Python 3.4.1 -- py-1.4.25 -- pytest-2.6.3 -- ...
> collected 6 items
> params/demo_ids.py::test_funcs_without_name[0] PASSED
> params/demo_ids.py::test_funcs_without_name[1] PASSED
> params/demo_ids.py::test_funcs_without_name[2] PASSED
> params/demo_ids.py::test_funcs_with_name[value of a] PASSED
> params/demo_ids.py::test_funcs_with_name[value of a] PASSED
> params/demo_ids.py::test_funcs_with_name[value of a] PASSED
> =========================== 6 passed in 0.02 seconds
> ===========================
> $


If I want to show both the value of each argument and its name, I can do
something like this:

def fn(n):
>     return range(n)
>
> @pytest.mark.parametrize('a', fn(3), ids=['a: {}'.format(i) for i in
> fn(3)])
> def test_funcs_with_naming_func(a):
>     assert a ** 3 == a * (a ** 2)


> params/demo_ids.py::test_funcs_with_naming_func[a: 0] PASSED
> params/demo_ids.py::test_funcs_with_naming_func[a: 1] PASSED
> params/demo_ids.py::test_funcs_with_naming_func[a: 2] PASSED


I can see to it that neither the argnames nor the argvalues appear more
than once in the set of parameters to pytest.markparametrize.

def params(n):

    fn = range(n)

    return {{'name': 'a', 'args': fn, 'ids': ['a: {}'.format(i) for i in
> fn]}


> named_args = params(3)


> @pytest.mark.parametrize(named_args['name'], pairs['args'], ids=pairs
> ['ids'])
> def test_funcs_with_naming_func(a):
>     assert a ** 3 == a * (a ** 2)


But I wonder if there is a more compact way to accomplish this within
Pytest itself, without the separate function

Thanks for your time.

- dpb
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