[python鼻子--with-doctest添加额外的测试

Question

我需要推迟某些库的导入，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)

我已经通过测试运行了nose，一切都通过了。但是，当我运行--with-doctest时，它将运行一个额外的测试（我尚未定义），该测试在未安装给定库的任何环境中都会产生错误。

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项测试。

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))

很明显，只有一个doctest可供测试。同样，如果安装了numpy，则仅运行1个测试。那么，为什么没有安装numpy时又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！

核心困难是doctest模块“诱使”您尝试进行numpy导入。也就是说，它探测了numpy.__wrapped__，然后您就上了诱饵。您需要区分一个探测调用，为此，可以返回一个虚拟值，和真实的电话，您必须为此输入或加注。

也许启发式测试__wrapped__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方，注意它是自动文档，并据此更改行为。