互斥关键字args的优雅模式? [英] Elegant pattern for mutually exclusive keyword args?

问题描述

有时候在我的代码中，我有一个函数可以用两种方式之一作为参数.像这样:

Sometimes in my code I have a function which can take an argument in one of two ways. Something like:

def func(objname=None, objtype=None):
    if objname is not None and objtype is not None:
        raise ValueError("only 1 of the ways at a time")
    if objname is not None:
        obj = getObjByName(objname)
    elif objtype is not None:
        obj = getObjByType(objtype)
    else:
        raise ValueError("not given any of the ways")

    doStuffWithObj(obj)

还有其他更优雅的方法吗?如果arg可以通过以下三种方式之一出现怎么办?如果类型不同，我可以这样做:

Is there any more elegant way to do this? What if the arg could come in one of three ways? If the types are distinct I could do:

def func(objnameOrType):
    if type(objnameOrType) is str:
        getObjByName(objnameOrType)
    elif type(objnameOrType) is type:
        getObjByType(objnameOrType)
    else:
        raise ValueError("unk arg type: %s" % type(objnameOrType))

但是如果不是的话该怎么办?这种选择似乎很愚蠢:

But what if they are not? This alternative seems silly:

def func(objnameOrType, isName=True):
    if isName:
        getObjByName(objnameOrType)
    else:
        getObjByType(objnameOrType)

这是因为您必须像 func(mytype，isName = False)这样称呼它，这很奇怪.

cause then you have to call it like func(mytype, isName=False) which is weird.

推荐答案

如何使用类似命令分发模式的内容:

How about using something like a command dispatch pattern:

def funct(objnameOrType):
   dispatcher = {str: getObjByName,
                 type1: getObjByType1,
                 type2: getObjByType2}
   t = type(objnameOrType)
   obj = dispatcher[t](objnameOrType)
   doStuffWithObj(obj)

其中 type1 ， type2 等是实际的python类型(例如int，float等).

where type1,type2, etc are actual python types (e.g. int, float, etc).

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