allow to pass argvalues as an iterator to pytest.mark.parametrize()

[pytestbot]

Originally reported by: Ronny Pfannschmidt (BitBucket: RonnyPfannschmidt, GitHub: RonnyPfannschmidt)

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• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/122

[pytestbot]

Original comment by Ronny Pfannschmidt (BitBucket: RonnyPfannschmidt, GitHub: RonnyPfannschmidt):

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i noticed a deeper issue,

just consuming the map object will break parametrizing anything that reuses it

[pytestbot]

Original comment by Rafał Stożek (BitBucket: rafales, GitHub: rafales):

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For anyone who will have the same issue: if you pass results of zip(), map(), range(), filter() etc. to a marker like parametrize make sure you wrap it in a list() call like this:

#!python

@pytest.mark.parametrize(('method',), list(zip(HTTP_METHODS)))
def test_foo(method):
    # code

because in python 3 those methods return a generator instead of a list.

[pytestbot]

Original comment by holger krekel (BitBucket: hpk42, GitHub: hpk42):

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pytest-trunk already handles the case when you use map/zip/range/filter in parametrize but as @RonnyPfannschmidt points out, if you apply the same marker instance multiple times you'll get a "skip" on the second application because the iterator is exhausted. I guess parametrize() should explode the values early on to avoid this issue.

[pytestbot]

Original comment by holger krekel (BitBucket: hpk42, GitHub: hpk42):

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clarify that pytest.mark.parametrize() takes a list of argvalues and not just
arbitrary iterators. Addresses issue122.

[pytestbot]

Original comment by holger krekel (BitBucket: hpk42, GitHub: hpk42):

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While params in @pytest.fixture(..., params=...) can be iterators, the parametrize marker requires lists (as opposed to iterators) in the general case. Allowing to use iterators requires an "early" explosion of the iterator so that the marker can be applied multiple times. Particularly on Python3 that would allow to use "range" or "map" for constructing the argvalues without the need to wrap them in a list. The latter is a bit surprising for newcomers.

[nicoddemus]

@hpk42 and @RonnyPfannschmidt, this works for me in Python 3.4 with the latest master:

import pytest
pp = pytest.mark.parametrize('i', range(3))

@pp
def test_foo(i):
    pass

@pp
def test_bar(i):
    pass 

py.test -v outputs:

test_foo.py::test_foo[0] PASSED
test_foo.py::test_foo[1] PASSED
test_foo.py::test_foo[2] PASSED
test_foo.py::test_bar[0] PASSED
test_foo.py::test_bar[1] PASSED
test_foo.py::test_bar[2] PASSED

I couldn't find anything in the CHANGELOG mentioning this issue. Is this still an issue, or can we close this?

[hpk42]

it still fails with examples like this:

import pytest

p = pytest.mark.parametrize("x", iter([1,2,3]))

@p 
def test_qwe(testdir, x):
     pass

@p
def test_qwe2(testdir, x):
    pass

[RonnyPfannschmidt]

@nicoddemus unlike general iterators, like for example map/imap objects, a range can be consumed multiple times

[nicoddemus]

@RonnyPfannschmidt oh I didn't know that, thanks!

[RonnyPfannschmidt]

Closing this one, as its messy to support and a actual user error, perhaps there should be a warning for non-sequences?