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警告是警报消息，它基本上不会引发异常，也不会终止程序。
警告类别如下所示：
| class | disposition |
|---|---|
| warning | this is the base class of all warning category classes. it is a subclass of exception. |
| userwarning | the default category for warn(). |
| deprecationwarning | base category for warnings about deprecated features when those warnings are intended for other python developers (ignored by default, unless triggered by code in __main__). |
| syntaxwarning | base category for warnings about dubious syntactic features. |
| runtimewarning | base category for warnings about dubious runtime features. |
| futurewarning | base category for warnings about deprecated features when those warnings are intended for end users of applications that are written in python. |
| pendingdeprecationwarning | base category for warnings about features that will be deprecated in the future (ignored by default). |
| importwarning | base category for warnings triggered during the process of importing a module (ignored by default). |
| unicodewarning | base category for warnings related to unicode. |
| unicodewarning | base category for warnings related to unicode. |
| byteswarning | base category for warnings related to bytes and bytearray. |
| resourcewarning | base category for warnings related to resource usage (ignored by default). |
warn() 可以手动发出警告，如下所示：
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*备忘录：
- 第一个参数是 message(required-type:str)。
- 第二个参数是类别（可选-默认：无-类型：警告）。 *如果为none，则设置userwarning。
- 第三个参数是 stacklevel（可选-默认：1-类型：int）。 *它决定警告所指的代码。
- 第四个参数是源（optional-default:none-type:any）。
- 有skip_file_prefixes参数（可选-默认：无-类型：str的元组）：
*备注：
- skip_file_prefixes=必须使用。
- 手动设置 none 会出错。
import warnings
warnings.warn(message="This is a warning.")
# UserWarning: This is a warning.
# warnings.warn(message="This is a warning.")
warnings.warn(message="This is a warning.",
category=None,
stacklevel=1,
source=None,
skip_file_prefixes=())
# UserWarning: This is a warning.
# warnings.warn(message="This is a warning.",
warnings.warn(message="This is a warning.",
category=Warning)
# Warning: This is a warning.
# warnings.warn(message="This is a warning.",
warnings.warn(message="This is a warning.",
category=DeprecationWarning)
# DeprecationWarning: This is a warning.
# warnings.warn(message="This is a warning.",
def test1():
warnings.warn(message="Warning 1",
stacklevel=-100)
warnings.warn(message="Warning 2",
stacklevel=0)
warnings.warn(message="Warning 3",
stacklevel=1)
warnings.warn(message="Warning 4",
stacklevel=2)
warnings.warn(message="Warning 5",
stacklevel=3)
warnings.warn(message="Warning 6",
stacklevel=4)
warnings.warn(message="Warning 7",
stacklevel=5)
warnings.warn(message="Warning 8",
stacklevel=100)
def test2():
test1()
def test3():
test2()
test3()
# UserWarning: Warning 1
# warnings.warn(message="Warning 1",
# UserWarning: Warning 2
# warnings.warn(message="Warning 2",
# UserWarning: Warning 3
# warnings.warn(message="Warning 3",
# UserWarning: Warning 4
# test1()
# UserWarning: Warning 5
# test2()
# UserWarning: Warning 6
# test3()
# UserWarning: Warning 7
# exec(code_obj, self.user_global_ns, self.user_ns)
# UserWarning: Warning 8
