Python 中的警告

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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：

*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

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