如何警告类（名称）弃用

也许我可以让 OldClsName 成为一个函数，它会发出警告（到日志）并从其参数构造 NewClsName 对象（使用 *args 和 **kvargs），但它看起来不够优雅（或者可能是？）。

是的，我认为这是非常标准的做法：

def OldClsName(*args, **kwargs):
    from warnings import warn
    warn("get with the program!")
    return NewClsName(*args, **kwargs)

唯一棘手的事情是，如果您有 OldClsName 的子类 - 那么我们必须变得聪明。如果您只需要保留对类方法的访问权限，则应该这样做：

class DeprecationHelper(object):
    def __init__(self, new_target):
        self.new_target = new_target

    def _warn(self):
        from warnings import warn
        warn("Get with the program!")

    def __call__(self, *args, **kwargs):
        self._warn()
        return self.new_target(*args, **kwargs)

    def __getattr__(self, attr):
        self._warn()
        return getattr(self.new_target, attr)

OldClsName = DeprecationHelper(NewClsName)

我尚未对其进行测试，但这应该会给您一些想法 - __call__ 将处理正常实例化路由，__getattr__ 将捕获对类方法的访问 &仍然会产生警告，而不会弄乱您的班级层次结构。

---

请查看warnings.warn。

如您所见，文档中的示例是一个弃用警告：

def deprecation(message):
    warnings.warn(message, DeprecationWarning, stacklevel=2)

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以下是解决方案应满足的要求列表：

不推荐使用的类的实例化应引发警告

不推荐使用的类的子类化应引发警告

支持 isinstance 和 issubclass 检查

解决方案

这可以通过自定义元类来实现：

class DeprecatedClassMeta(type):
    def __new__(cls, name, bases, classdict, *args, **kwargs):
        alias = classdict.get('_DeprecatedClassMeta__alias')

        if alias is not None:
            def new(cls, *args, **kwargs):
                alias = getattr(cls, '_DeprecatedClassMeta__alias')

                if alias is not None:
                    warn("{} has been renamed to {}, the alias will be "
                         "removed in the future".format(cls.__name__,
                             alias.__name__), DeprecationWarning, stacklevel=2)

                return alias(*args, **kwargs)

            classdict['__new__'] = new
            classdict['_DeprecatedClassMeta__alias'] = alias

        fixed_bases = []

        for b in bases:
            alias = getattr(b, '_DeprecatedClassMeta__alias', None)

            if alias is not None:
                warn("{} has been renamed to {}, the alias will be "
                     "removed in the future".format(b.__name__,
                         alias.__name__), DeprecationWarning, stacklevel=2)

            # Avoid duplicate base classes.
            b = alias or b
            if b not in fixed_bases:
                fixed_bases.append(b)

        fixed_bases = tuple(fixed_bases)

        return super().__new__(cls, name, fixed_bases, classdict,
                               *args, **kwargs)

    def __instancecheck__(cls, instance):
        return any(cls.__subclasscheck__(c)
            for c in {type(instance), instance.__class__})

    def __subclasscheck__(cls, subclass):
        if subclass is cls:
            return True
        else:
            return issubclass(subclass, getattr(cls,
                              '_DeprecatedClassMeta__alias'))

解释

DeprecatedClassMeta.__new__ 方法不仅为它是元类的类调用，而且为该类的每个子类调用。这提供了确保 DeprecatedClass 的任何实例都不会被实例化或子类化的机会。

实例化很简单。元类覆盖 DeprecatedClass 的 __new__ 方法以始终返回 NewClass 的实例。

子类化并不难。 DeprecatedClassMeta.__new__ 接收基类列表并需要将 DeprecatedClass 的实例替换为 NewClass。

最后，通过 PEP 3119 中定义的 __instancecheck__ 和 __subclasscheck__ 实现 isinstance 和 issubclass 检查。

测试

class NewClass:
    foo = 1


class NewClassSubclass(NewClass):
    pass


class DeprecatedClass(metaclass=DeprecatedClassMeta):
    _DeprecatedClassMeta__alias = NewClass


class DeprecatedClassSubclass(DeprecatedClass):
    foo = 2


class DeprecatedClassSubSubclass(DeprecatedClassSubclass):
    foo = 3


assert issubclass(DeprecatedClass, DeprecatedClass)
assert issubclass(DeprecatedClassSubclass, DeprecatedClass)
assert issubclass(DeprecatedClassSubSubclass, DeprecatedClass)
assert issubclass(NewClass, DeprecatedClass)
assert issubclass(NewClassSubclass, DeprecatedClass)

assert issubclass(DeprecatedClassSubclass, NewClass)
assert issubclass(DeprecatedClassSubSubclass, NewClass)

assert isinstance(DeprecatedClass(), DeprecatedClass)
assert isinstance(DeprecatedClassSubclass(), DeprecatedClass)
assert isinstance(DeprecatedClassSubSubclass(), DeprecatedClass)
assert isinstance(NewClass(), DeprecatedClass)
assert isinstance(NewClassSubclass(), DeprecatedClass)

assert isinstance(DeprecatedClassSubclass(), NewClass)
assert isinstance(DeprecatedClassSubSubclass(), NewClass)

assert NewClass().foo == 1
assert DeprecatedClass().foo == 1
assert DeprecatedClassSubclass().foo == 2
assert DeprecatedClassSubSubclass().foo == 3

---

在 python >= 3.6 中，您可以轻松处理子类化警告：

class OldClassName(NewClassName):
    def __init_subclass__(self):
        warn("Class has been renamed NewClassName", DeprecationWarning, 2)

重载 __new__ 应该允许您在直接调用旧类构造函数时发出警告，但我没有测试过，因为我现在不需要它。

---

从 Python 3.7 开始，您可以使用 __getattr__（和 __dir__）提供对模块属性访问的自定义。 PEP 562 中解释了所有内容。在下面的示例中，我实现了 __getattr__ 和 __dir__ 以弃用“OldClsName”以支持“NewClsNam”：

# your_lib.py

import warnings

__all__ = ["NewClsName"]

DEPRECATED_NAMES = [('OldClsName', 'NewClsName')]


class NewClsName:
    @classmethod
    def create_variant1(cls):
        return cls()


def __getattr__(name):
    for old_name, new_name in DEPRECATED_NAMES:
        if name == old_name:
            warnings.warn(f"The '{old_name}' class or function is renamed '{new_name}'",
                          DeprecationWarning,
                          stacklevel=2)
            return globals()[new_name]
    raise AttributeError(f"module {__name__} has no attribute {name}")


def __dir__():
    return sorted(__all__ + [names[0] for names in DEPRECATED_NAMES])

在 __getattr__ 函数中，如果发现不推荐使用的类或函数名称，则会发出警告消息，显示调用者的源文件和行号（带有 stacklevel=2）。

在用户代码中，我们可以：

# your_lib_usage.py
from your_lib import NewClsName
from your_lib import OldClsName


def use_new_class():
    obj = NewClsName.create_variant1()
    print(obj.__class__.__name__ + " is created in use_new_class")


def use_old_class():
    obj = OldClsName.create_variant1()
    print(obj.__class__.__name__ + " is created in use_old_class")


if __name__ == '__main__':
    use_new_class()
    use_old_class()

当用户运行他的脚本 your_lib_usage.py 时，它将得到如下内容：

NewClsName is created in use_new_class
NewClsName is created in use_old_class
/path/to/your_lib_usage.py:3: DeprecationWarning: The 'OldClsName' class or function is renamed 'NewClsName'
  from your_lib import OldClsName

注意：堆栈跟踪通常用 STDERR 编写。

要查看错误警告，您可能需要在 Python 命令行中添加“-W”标志，例如：

python -W always your_lib_usage.py

---

你为什么不只是子类？这样就不应该破坏任何用户代码。

class OldClsName(NewClsName):
    def __init__(self, *args, **kwargs):
        warnings.warn("The 'OldClsName' class was renamed [...]",
                      DeprecationWarning)
        NewClsName.__init__(*args, **kwargs)

---

使用 inspect 模块为 OldClass 添加占位符，然后 OldClsName is NewClsName 检查将通过，并且 pylint 之类的 linter 会将此通知为错误。

弃用.py

import inspect
import warnings
from functools import wraps

def renamed(old_name):
    """Return decorator for renamed callable.

    Args:
        old_name (str): This name will still accessible,
            but call it will result a warn.

    Returns:
        decorator: this will do the setting about `old_name`
            in the caller's module namespace.
    """

    def _wrap(obj):
        assert callable(obj)

        def _warn():
            warnings.warn('Renamed: {} -> {}'
                        .format(old_name, obj.__name__),
                        DeprecationWarning, stacklevel=3)

        def _wrap_with_warn(func, is_inspect):
            @wraps(func)
            def _func(*args, **kwargs):
                if is_inspect:
                    # XXX: If use another name to call,
                    # you will not get the warning.
                    frame = inspect.currentframe().f_back
                    code = inspect.getframeinfo(frame).code_context
                    if [line for line in code
                            if old_name in line]:
                        _warn()
                else:
                    _warn()
                return func(*args, **kwargs)
            return _func

        # Make old name available.
        frame = inspect.currentframe().f_back
        assert old_name not in frame.f_globals, (
            'Name already in use.', old_name)

        if inspect.isclass(obj):
            obj.__init__ = _wrap_with_warn(obj.__init__, True)
            placeholder = obj
        else:
            placeholder = _wrap_with_warn(obj, False)

        frame.f_globals[old_name] = placeholder

        return obj

    return _wrap

测试.py

from __future__ import print_function

from deprecate import renamed


@renamed('test1_old')
def test1():
    return 'test1'


@renamed('Test2_old')
class Test2(object):
    pass

    def __init__(self):
        self.data = 'test2_data'

    def method(self):
        return self.data

# pylint: disable=undefined-variable
# If not use this inline pylint option, 
# there will be E0602 for each old name.
assert(test1() == test1_old())
assert(Test2_old is Test2)
print('# Call new name')
print(Test2())
print('# Call old name')
print(Test2_old())

然后运行 python -W all test.py：

test.py:22: DeprecationWarning: Renamed: test1_old -> test1
# Call new name
<__main__.Test2 object at 0x0000000007A147B8>
# Call old name
test.py:27: DeprecationWarning: Renamed: Test2_old -> Test2
<__main__.Test2 object at 0x0000000007A147B8>

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