python nose --with-doctest 添加额外的测试

Question

我需要推迟一些库的导入，除非需要它们，所以我创建了一个对象来推迟导入。

class Importer(object):
    def __init__(self, name):
        self.name = name

    def __bool__(self):
        try:
            mod = importlib.import_module(self.name)
            return True
        except ImportError:
            return False

    def __getattr__(self, name):
        try:
            mod = importlib.import_module(self.name)
            attr = getattr(mod, name)
            setattr(self, name, attr)
            return attr
        except ImportError as e:
            msg = self.name + " must be installed"
            raise ImportError(msg)

我的测试已经运行nose，一切都通过了。但是，当我运行 --with-doctest 时，它会运行一个额外的测试（我尚未定义），该测试会在未安装给定库的任何环境中生成错误。

测试下面的代码会重现我遇到的问题。在没有numpy 的环境中，nosetests --with-doctest 正在运行我尚未定义的第二个测试。

numpy = Importer('numpy')

def mean(array):
    """
    Mean of an array.

    Examples
    --------
    >>> mean([1, 2, 3])
    2.0
    >>> mean([1, -1])
    0.0
    """
    if numpy:
        return numpy.mean(array)
    return float(sum(array) / len(array))

显然，只有一个 doctest 可供测试。此外，如果安装了numpy，则仅运行 1 个测试。那么为什么当没有安装numpy 时我要进行第二次测试呢？这是输出。

.E
======================================================================
ERROR: Failure: ImportError (numpy must be installed)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/devin/Dropbox/Devin_S_+_Spark_Wave/nimble/zissue/issue.py", line 16, in __getattr__
    mod = importlib.import_module(self.name)
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 953, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'numpy'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/site-packages/nose/failure.py", line 39, in runTest
    raise self.exc_val.with_traceback(self.tb)
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/site-packages/nose/plugins/manager.py", line 154, in generate
    for r in result:
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/site-packages/nose/plugins/doctests.py", line 228, in loadTestsFromModule
    tests = self.finder.find(module)
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/doctest.py", line 933, in find
    self._find(tests, obj, name, module, source_lines, globs, {})
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/doctest.py", line 992, in _find
    if ((inspect.isroutine(inspect.unwrap(val))
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/inspect.py", line 512, in unwrap
    while _is_wrapper(func):
  File "/Users/devin/anaconda3/envs/issueEnv/lib/python3.6/inspect.py", line 503, in _is_wrapper
    return hasattr(f, '__wrapped__')
  File "/Users/devin/Dropbox/testing/issue/issue.py", line 22, in __getattr__
    raise ImportError(msg)
ImportError: numpy must be installed

----------------------------------------------------------------------
Ran 2 tests in 0.003s

Answer 1

嗯，这很有趣！

核心困难在于doctest 模块“欺骗”了您尝试 numpy 导入。 也就是说，它探测了numpy.__wrapped__，而你上钩了。 您需要区分探测调用， 返回一个虚拟值是可以接受的， 和一个真正的跟注，你必须为此引入或加注。

也许对__wrapped__ 进行启发式测试就足够了。 但是您可能会发现有必要检查调用堆栈以找到调用者， 注意它是例如自动文档， 并据此改变行为。