根据自定义警告类别过滤

Question

除了预先存在的警告类别，用户还可以define their own warning classes，例如在下面的代码中：

$ cat mwe.py 
#!/usr/bin/env python3.5

import warnings
import pprint

class ObnoxiousWarning(UserWarning):
    pass

for i in range(3):
    print(i)
    warnings.warn("I don't like this.", ObnoxiousWarning)

调用Python时，-W flag controls how to filter warnings。但是当我试图让它忽略我刚创建的警告类别时，我被告知过滤器被忽略了：

$ python3.5 -W ignore::ObnoxiousWarning ./mwe.py
Invalid -W option ignored: unknown warning category: 'ObnoxiousWarning'
0
./mwe.py:11: ObnoxiousWarning: I don't like this.
  warnings.warn("I don't like this.", ObnoxiousWarning)
1
2

如何使用命令行为自定义警告类别插入过滤器（而不是我可以执行的所有 UserWarnings 或基于警告消息的过滤）？

编辑 2018-11-29：参见 Issue 22543: -W option cannot use nonstandard categories

Answer 1

部分答案在 python 源代码中。查看 _getcategory 函数： https://github.com/python/cpython/blob/3.5/Lib/warnings.py#L147

def _getcategory(category):
    import re
    if not category:
        return Warning
    if re.match("^[a-zA-Z0-9_]+$", category):
        try:
            cat = eval(category)
        except NameError:
            raise _OptionError("unknown warning category: %r" % (category,))
    else:
        i = category.rfind(".")
        module = category[:i]
        klass = category[i+1:]
        try:
            m = __import__(module, None, None, [klass])
        except ImportError:
            raise _OptionError("invalid module name: %r" % (module,))
        try:
            cat = getattr(m, klass)
        except AttributeError:
            raise _OptionError("unknown warning category: %r" % (category,))
    if not issubclass(cat, Warning):
        raise _OptionError("invalid warning category: %r" % (category,))
    return cat

Python 尝试评估您的类别或从您在过滤器中指定的模块导入它。这将失败，除非你的模块在 PYTHONPATH 中。

PYTHONPATH='<path_to_dir_where_mwe_located>' python -W ignore::mwe.ObnoxiousWarning

这样，如果您在 python shell 中导入模块，警告将按您的意愿过滤。要在命令行中使用过滤器，您必须在单独的模块中定义您的警告，而不是您执行的模块。

mwe.py

class ObnoxiousWarning(UserWarning):
    pass

entrypoint.py

#!/usr/bin/env python3.5

import warnings
import pprint

from mwe import ObnoxiousWarning

for i in range(3):
    print(i)
    warnings.warn("I don't like this.", ObnoxiousWarning)

最后：

PYTHONPATH='<path_to_dir_where_mwe_located>' python -W ignore::mwe.ObnoxiousWarning ./entrypoint.py
0
1
2

我不明白为什么定义带有警告的单独模块有效，但确实如此。可能有人会解释一下。

根据自定义警告类别过滤

Filtering based on custom warning categories

python

warnings