Python 如何让tox在运行测试时尊重系统版本？

我有一些代码，其中控制逻辑根据python2和python3进行更改。我也在用tox测试这个，当我意识到：

• tox没有在测试中使用正确的sys.version\u info.major，它使用运行tox命令时使用的任何python版本

MVCE可以在下面显示，其中三个文件位于同一目录中：

setup.py

from setuptools import setup
if __name__ == '__main__':
    setup(name='throwaway')

import sys
import unittest


class tester(unittest.TestCase):

    def test_version(self):
        self.assertEqual(2, sys.version_info.major)

dev_requirements.txt

nose

tox.ini

[tox]
envlist=py{27,3.6}
[testenv]
deps=-rdev_requirements.txt
commands=
   nosetests 

测试版本.py

from setuptools import setup
if __name__ == '__main__':
    setup(name='throwaway')

import sys
import unittest


class tester(unittest.TestCase):

    def test_version(self):
        self.assertEqual(2, sys.version_info.major)

当在python3.6设置中运行时，该测试用例应该失败，但是，当使用

tox

命令运行时：

$python --version
Python 2.7.13
$tox
GLOB sdist-make: /Users/username/tmp/toxtesting/setup.py
py27 create: /Users/username/tmp/toxtesting/.tox/py27
py27 installdeps: -rdev_requirements.txt
py27 inst: /Users/username/tmp/toxtesting/.tox/dist/throwaway-0.0.0.zip
py27 installed: appdirs==1.4.3,nose==1.3.7,packaging==16.8,pyparsing==2.2.0,six==1.10.0,throwaway==0.0.0
py27 runtests: PYTHONHASHSEED='3463719492'
py27 runtests: commands[0] | nosetests
.
----------------------------------------------------------------------
Ran 1 test in 0.002s

OK
py3.6 create: /Users/username/tmp/toxtesting/.tox/py3.6
py3.6 installdeps: -rdev_requirements.txt
py3.6 inst: /Users/username/tmp/toxtesting/.tox/dist/throwaway-0.0.0.zip
py3.6 installed: appdirs==1.4.3,nose==1.3.7,packaging==16.8,pyparsing==2.2.0,six==1.10.0,throwaway==0.0.0
py3.6 runtests: PYTHONHASHSEED='3463719492'
py3.6 runtests: commands[0] | nosetests
.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK
___________________________________________________________________________________ summary ____________________________________________________________________________________
  py27: commands succeeded
  py3.6: commands succeeded
  congratulations :)

---

当使用Python2.7运行时，tox将在其所有配置中使用该环境（如示例所示）

但是，如果使用python3环境运行tox：

$python --version
Python 3.6.0

$tox 
GLOB sdist-make: /Users/username/tmp/toxtesting/setup.py
py27 create: /Users/username/tmp/toxtesting/.tox/py27
py27 installdeps: -rdev_requirements.txt
py27 inst: /Users/username/tmp/toxtesting/.tox/dist/throwaway-0.0.0.zip
py27 installed: appdirs==1.4.3,nose==1.3.7,packaging==16.8,pyparsing==2.2.0,six==1.10.0,throwaway==0.0.0
py27 runtests: PYTHONHASHSEED='595957228'
py27 runtests: commands[0] | nosetests
.
----------------------------------------------------------------------
Ran 1 test in 0.003s

OK
py3.6 create: /Users/username/tmp/toxtesting/.tox/py3.6
py3.6 installdeps: -rdev_requirements.txt
py3.6 inst: /Users/username/tmp/toxtesting/.tox/dist/throwaway-0.0.0.zip
py3.6 installed: appdirs==1.4.3,nose==1.3.7,packaging==16.8,pyparsing==2.2.0,six==1.10.0,throwaway==0.0.0
py3.6 runtests: PYTHONHASHSEED='595957228'
py3.6 runtests: commands[0] | nosetests
F
======================================================================
FAIL: test_version (test_versions.tester)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/username/tmp/toxtesting/test_versions.py", line 8, in test_version
    self.assertEqual(2, sys.version_info.major)
AssertionError: 2 != 3

----------------------------------------------------------------------
Ran 1 test in 0.003s

FAILED (failures=1)
ERROR: InvocationError: '/Users/username/tmp/toxtesting/.tox/py3.6/bin/nosetests'
___________________________________________________________________________________ summary ____________________________________________________________________________________
  py27: commands succeeded
ERROR:   py3.6: commands failed

---

将看到预期的行为，其中

sys.version\u info

在python2.7和python3.6两个版本之间都是正确的。

请尝试环境名称中的“36”而不是“3.6”。如果这无助于为您的环境声明basepython：

[testenv]
basepython =
    py27: python2.7
    py36: python3.6

添加comand以显示python版本：

commands =
    {envpython} --version

我通常在[testenv]中添加命令，并从其他测试部分调用它，如下所示：

[testenv]
…
commands =
    {envpython} --version

[mytest]
commands =
    {[testenv]commands}
    … other test commnds …