Question

我正在尝试将一个“子命令”系统实现为Python中的可继承类。我的预期用例类似于：

from command import Command
import sys

class MyCommand(Command):
    @Command.subcommand
    def foo(self):
        print "this can be run as a subcommand"

    def bar(self):
        print "but this is a plain method and isn't exposed to the CLI"

MyCommand()(*sys.argv)

# at the command line, the user runs "mycommand.py foo"

我将Command.subcommand实现为静态方法，一切正常，直到我尝试将子命令添加到父类，这得到了TypeError: 'staticmethod' object is not callable。事后看来，this显然不起作用：

class Command(object):
    @staticmethod
    def subcommand(method):
        method.is_subcommand = True

        return method

    @subcommand
    def common(self):
        print "this subcommand is available to all child classes"

到目前为止，我发现的唯一替代方法是在父类之外声明subcommand装饰器，然后在类定义完成后将其注入。

def subcommand(method):
    method.is_subcommand = True

    return method

class Command(object):
    @subcommand
    def common(self):
        print "this subcommand is available to all child classes"

Command.subcommand = staticmethod(subcommand)
del subcommand

然而，作为在添加装饰者之前从未使用过Python的人，这对我来说非常笨重。有没有更优雅的方法来实现这一目标？

Answer 1

我能想到这个问题有两个解决方案。最简单的方法是在完成后在父类中使用它，使其成为静态方法：

class Command(object): def subcommand(method): # Regular function in class definition scope. method.is_subcommand = True return method @subcommand def common(self): print "this subcommand is available to all child classes" subcommand = staticmethod(subcommand) # Now a static method. Can no longer be called during class definition phase.

这有点脆弱，因为在将它作为静态方法后，不能在父类中使用它。更强大的方法是添加一个中间类：

class Command(object): @staticmethod def subcommand(method): method.is_subcommand = True return method class CommandBase(Command): @Command.subcommand def common(self): print "this subcommand is available to all child classes"

您现在可以从CommandBase而不是Command继承所有课程。

在类中定义装饰器，这也可以在类定义中使用

1 个答案: