python - 最简单的方法来 "store"一个类上的函数而不绑定(bind)它？

Question

我正在编写一些支持代码以加快通过 RequestFactory 调用 Django View (在别处声明的函数)。我将大部分测试属性直接存储在类上，而不是它们的实例上。

我必须做的一件事是在类中存储我感兴趣的函数，以便稍后调用它(使用 inspect 为其提供正确的参数)。

这是我的总体意图:

def to_test(var1, var2, var3):
    "this function has nothing to do with MyTest"
    assert isinstance(var1, basestring), "not an instance"

class MyTest(unittest.TestCase):

    #only using this attribute to store the function to 
    #test, not to bind that function
    func_under_test = to_test

    def test_with_abc(self):
        self.func_under_test("a","b", "c")

    def test_with_def(self):
        self.func_under_test("d","e", "f")

但是一旦我将一个函数分配给一个类，它就会绑定(bind)到该类。

这在 99% 的时间里都很棒。只是不在这里，因为它在调用时得到了错误的参数。相反，在每个类上我都重新声明某物，以便我可以将函数分配给它，而不是直接在类上。甚至元类也无济于事。

一些示例代码

我想要的是 FunctionStore1/2 的语法。我实际上最接近的是 FunctionStore3/4/6，但它们要求您每次都记住复制和粘贴小的 _ 声明。没什么大不了的，只是 hacky。

def regular_function(*args, **kwds):
    print ("    regular_function(%s)" % (locals()))

def regular_function2(*args, **kwds):
    print ("    regular_function2(%s)" % (locals()))

class FunctionStore1(object):
    "this fails, expecting an instance"
    func_to_check = regular_function

class FunctionStore2(object):
    "ditto"
    func_to_check = regular_function2

class FunctionStore3Works(object):
    "this works"

    def _(): pass
    _.func_to_check = regular_function


class FunctionStore4Works(object):
    """this too, but I have to redeclare the `_` each time
       can I use MetaClass?
    """

    def _(): pass
    _.func_to_check = regular_function2

class BaseTsupporter(object):
    "this doesnt help..."
    def _(): pass

class FunctionStore5(BaseTsupporter):
    "because there is no `_` here"

    try:
        _.func_to_check = regular_function
    except Exception, e:
            print ("\nno `_` on FunctionStore5:e:%s" % (e))

class FunctionStore6Works(object):
    "trying a dict"

    _ = dict(func_to_check=regular_function)

class MyMeta(type):
    def __new__(meta, name, bases, dct):
        res = super(MyMeta, meta).__new__(meta, name, bases, dct)
        #this works...
        res._ = dict()
        return res

    def __init__(cls, name, bases, dct):
        super(MyMeta, cls).__init__(name, bases, dct)

try:
    class FunctionStore7Meta(object):
        "using meta"

        __metaclass__ = MyMeta

        try:
            _.update(func_to_check=regular_function)                
        except Exception, e:
            print ("\nno `_` dict on FunctionStore7:e:%s" % (e))

except Exception, e:
    print ("\nno luck creating FunctionStore7 class :( exception:\n  %s" % (e))

#never mind the locals() + globals() hack, that's because this code is actually in a function to 
#allow SO's indenting...
li_to_call = [(k,v) for k, v in (locals().items() + globals().items()) if k.startswith("FunctionStore")]
li_to_call.sort()

for name, cls_ in li_to_call:
    print ("\n calling %s" % (name))
    try:
        if getattr(cls_, "func_to_check", None):
            cls_.func_to_check(name)
        elif hasattr(cls_, "_") and hasattr(cls_._, "func_to_check"):
            cls_._.func_to_check(name)
        elif hasattr(cls_, "_") and isinstance(cls_._, dict) and cls_._.get("func_to_check"):
            cls_._["func_to_check"](name)
        else:
            print ("    %s: no func_to_check" % (name))

            if "Meta" in name:
                print("        even if %s does have a `_`, now:%s" % (name, cls_._))

    except Exception, e:
            print ("    %s: exception:%s" % (name, e))

输出:

no `_` on FunctionStore5:e:name '_' is not defined

no `_` dict on FunctionStore7:e:name '_' is not defined

 calling FunctionStore1
    FunctionStore1: exception:unbound method regular_function() must be called with FunctionStore1 instance as first argument (got str instance instead)

 calling FunctionStore2
    FunctionStore2: exception:unbound method regular_function2() must be called with FunctionStore2 instance as first argument (got str instance instead)

 calling FunctionStore3Works
    regular_function({'args': ('FunctionStore3Works',), 'kwds': {}})

 calling FunctionStore4Works
    regular_function2({'args': ('FunctionStore4Works',), 'kwds': {}})

 calling FunctionStore5
    FunctionStore5: no func_to_check

 calling FunctionStore6Works
    regular_function({'args': ('FunctionStore6Works',), 'kwds': {}})

 calling FunctionStore7Meta
    FunctionStore7Meta: no func_to_check
        even if FunctionStore7Meta does have a `_`, now:{}

Answer 1

您可以将函数包装在 staticmethod 中:

class FunctionStore1(object):
    "this fails, expecting an instance"
    func_to_check = staticmethod(regular_function)