如何在对象的多个方法上使用 functools.partial 并无序冻结参数？

Question

我发现 functools.partial 非常有用，但我希望能够无序地冻结参数（您想要冻结的参数并不总是第一个）并且我希望能够将其应用于多个一次在一个类上使用方法，以创建一个代理对象，它与底层对象具有相同的方法，除了它的一些方法参数被冻结（将其视为泛化部分以应用于类）。我更愿意在不编辑原始对象的情况下执行此操作，就像部分不会更改其原始功能一样。

我设法拼凑了一个名为“bind”的 functools.partial 版本，它允许我通过关键字参数传递参数来乱序指定参数。这部分有效：

>>> def foo(x, y):
...     print x, y
...
>>> bar = bind(foo, y=3)
>>> bar(2)
2 3

但是我的代理类不起作用，我不确定为什么：

>>> class Foo(object):
...     def bar(self, x, y):
...             print x, y
...
>>> a = Foo()
>>> b = PureProxy(a, bar=bind(Foo.bar, y=3))
>>> b.bar(2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: bar() takes exactly 3 arguments (2 given)

我可能做错了，因为我只是按照我从随机文档、博客和中拼凑出来的内容进行操作在所有部分上运行 dir() 。关于如何使这项工作以及更好的实现方法的建议将不胜感激；）我不确定的一个细节是这应该如何与描述符交互。代码如下。

from types import MethodType

class PureProxy(object):
    def __init__(self, underlying, **substitutions):
        self.underlying = underlying

        for name in substitutions:
            subst_attr = substitutions[name]
            if hasattr(subst_attr, "underlying"):
                setattr(self, name, MethodType(subst_attr, self, PureProxy))

    def __getattribute__(self, name):
        return getattr(object.__getattribute__(self, "underlying"), name)

def bind(f, *args, **kwargs):
    """ Lets you freeze arguments of a function be certain values. Unlike
    functools.partial, you can freeze arguments by name, which has the bonus
    of letting you freeze them out of order. args will be treated just like
    partial, but kwargs will properly take into account if you are specifying
    a regular argument by name. """
    argspec = inspect.getargspec(f)
    argdict = copy(kwargs)

    if hasattr(f, "im_func"):
        f = f.im_func

    args_idx = 0
    for arg in argspec.args:
        if args_idx >= len(args):
            break

        argdict[arg] = args[args_idx]
        args_idx += 1

    num_plugged = args_idx

    def new_func(*inner_args, **inner_kwargs):
        args_idx = 0
        for arg in argspec.args[num_plugged:]:
            if arg in argdict:
                continue
            if args_idx >= len(inner_args):
                # We can't raise an error here because some remaining arguments
                # may have been passed in by keyword.
                break
            argdict[arg] = inner_args[args_idx]
            args_idx += 1

        f(**dict(argdict, **inner_kwargs))

    new_func.underlying = f

    return new_func

更新：如果任何人都可以受益，这是我采用的最终实现：

from types import MethodType

class PureProxy(object):
    """ Intended usage:
    >>> class Foo(object):
    ...     def bar(self, x, y):
    ...             print x, y
    ...
    >>> a = Foo()
    >>> b = PureProxy(a, bar=FreezeArgs(y=3))
    >>> b.bar(1)
    1 3
    """

    def __init__(self, underlying, **substitutions):
        self.underlying = underlying

        for name in substitutions:
            subst_attr = substitutions[name]
            if isinstance(subst_attr, FreezeArgs):
                underlying_func = getattr(underlying, name)
                new_method_func = bind(underlying_func, *subst_attr.args, **subst_attr.kwargs)
                setattr(self, name, MethodType(new_method_func, self, PureProxy))

    def __getattr__(self, name):
        return getattr(self.underlying, name)

class FreezeArgs(object):
    def __init__(self, *args, **kwargs):
        self.args = args
        self.kwargs = kwargs

def bind(f, *args, **kwargs):
    """ Lets you freeze arguments of a function be certain values. Unlike
    functools.partial, you can freeze arguments by name, which has the bonus
    of letting you freeze them out of order. args will be treated just like
    partial, but kwargs will properly take into account if you are specifying
    a regular argument by name. """
    argspec = inspect.getargspec(f)
    argdict = copy(kwargs)

    if hasattr(f, "im_func"):
        f = f.im_func

    args_idx = 0
    for arg in argspec.args:
        if args_idx >= len(args):
            break

        argdict[arg] = args[args_idx]
        args_idx += 1

    num_plugged = args_idx

    def new_func(*inner_args, **inner_kwargs):
        args_idx = 0
        for arg in argspec.args[num_plugged:]:
            if arg in argdict:
                continue
            if args_idx >= len(inner_args):
                # We can't raise an error here because some remaining arguments
                # may have been passed in by keyword.
                break
            argdict[arg] = inner_args[args_idx]
            args_idx += 1

        f(**dict(argdict, **inner_kwargs))

    return new_func

Answer 1

您“绑定太深”：将 PureProxydef __getattribute__(self, name): 更改为 def __getattr__(self, name): >。 __getattribute__ 拦截每个属性访问，因此绕过您使用 setattr(self, name, ...) 设置的所有内容，使这些 setattr 失去任何效果，这显然不是您想要的； __getattr__ 仅用于访问未另行定义的属性，因此这些 setattr 调用将成为“有效” 是

在该覆盖的正文中，您可以而且应该将 object.__getattribute__(self, "underlying") 更改为 self.underlying （因为您 不再覆盖 __getattribute__ 我建议进行其他更改（enumerate 代替您用于计数器等的低级逻辑），但它们不会改变语义。

通过我建议的更改，您的示例代码可以工作（当然，您必须继续测试更微妙的情况），我调试它的方式只是坚持 print< 。 /code> 语句放在适当的位置（侏罗纪=时代的方法，但仍然是我最喜欢的；-）。