问题：在Python中，如何将警告视为异常？

我在python代码中使用的第三方库（用C编写）正在发出警告。我希望能够使用try except语法正确处理这些警告。有没有办法做到这一点？

点击查看英文原文

A third-party library (written in C) that I use in my python code is issuing warnings. I want to be able to use the try except syntax to properly handle these warnings. Is there a way to do this?

回答 0

引用python手册（27.6.4。Testing Warnings）：

import warnings

def fxn():
    warnings.warn("deprecated", DeprecationWarning)

with warnings.catch_warnings(record=True) as w:
    # Cause all warnings to always be triggered.
    warnings.simplefilter("always")
    # Trigger a warning.
    fxn()
    # Verify some things
    assert len(w) == 1
    assert issubclass(w[-1].category, DeprecationWarning)
    assert "deprecated" in str(w[-1].message)
点击查看英文原文

To quote from the python handbook (27.6.4. Testing Warnings):

import warnings

def fxn():
    warnings.warn("deprecated", DeprecationWarning)

with warnings.catch_warnings(record=True) as w:
    # Cause all warnings to always be triggered.
    warnings.simplefilter("always")
    # Trigger a warning.
    fxn()
    # Verify some things
    assert len(w) == 1
    assert issubclass(w[-1].category, DeprecationWarning)
    assert "deprecated" in str(w[-1].message)

回答 1

要将警告作为错误处理，只需使用以下命令：

import warnings
warnings.filterwarnings("error")

之后，您将能够捕获与错误相同的警告，例如，它将起作用：

try:
    some_heavy_calculations()
except RuntimeWarning:
    import ipdb; ipdb.set_trace()

PS添加了此答案，因为注释中的最佳答案包含拼写错误：filterwarnigns而不是filterwarnings。

点击查看英文原文

To handle warnings as errors simply use this:

import warnings
warnings.filterwarnings("error")

After this you will be able to catch warnings same as errors, e.g. this will work:

try:
    some_heavy_calculations()
except RuntimeWarning:
    import ipdb; ipdb.set_trace()

P.S. Added this answer because the best answer in comments contains misspelling: filterwarnigns instead of filterwarnings.

回答 2

如果只希望脚本在警告上失败，则可以使用：

python -W error foobar.py
点击查看英文原文

If you just want you script to fail on warnings you can invoke python with the -W argument:

python -W error foobar.py

回答 3

这是一个变体，可让您更清楚地了解如何仅使用自定义警告。

import warnings
with warnings.catch_warnings(record=True) as w:
    # Cause all warnings to always be triggered.
    warnings.simplefilter("always")

    # Call some code that triggers a custom warning.
    functionThatRaisesWarning()

    # ignore any non-custom warnings that may be in the list
    w = filter(lambda i: issubclass(i.category, UserWarning), w)

    if len(w):
        # do something with the first warning
        email_admins(w[0].message)
点击查看英文原文

Here’s a variation that makes it clearer how to work with only your custom warnings.

import warnings
with warnings.catch_warnings(record=True) as w:
    # Cause all warnings to always be triggered.
    warnings.simplefilter("always")

    # Call some code that triggers a custom warning.
    functionThatRaisesWarning()

    # ignore any non-custom warnings that may be in the list
    w = filter(lambda i: issubclass(i.category, UserWarning), w)

    if len(w):
        # do something with the first warning
        email_admins(w[0].message)

回答 4

在某些情况下，您需要使用ctypes将警告变成错误。例如：

str(b'test')  # no error
import warnings
warnings.simplefilter('error', BytesWarning)
str(b'test')  # still no error
import ctypes
ctypes.c_int.in_dll(ctypes.pythonapi, 'Py_BytesWarningFlag').value = 2
str(b'test')  # this raises an error
点击查看英文原文

In some cases, you need use ctypes to turn warnings into errors. For example:

str(b'test')  # no error
import warnings
warnings.simplefilter('error', BytesWarning)
str(b'test')  # still no error
import ctypes
ctypes.c_int.in_dll(ctypes.pythonapi, 'Py_BytesWarningFlag').value = 2
str(b'test')  # this raises an error
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