Python3.4 ** kwargs，意外的关键字参数

Question

I have a dictionary of functions, all of which use 1 or 2 optional arguments. I want to iterate through this dictionary and pass both arguments to each iterated function, and have the functions that only need 1 argument to ignore the second. In these cases, however, I get an unexpected keyword argument error.

def getNumFrames(self, **kwargs):
    return len(self.x)

def getConcentration(self, **kwargs):
    if ((not gradient) or (not maxX)):
        return 0
    return (gradient / maxX) * self.x[0]

fields = {'numFrames': getNumFrames, 'concentration': getConcentration}


for field, fieldFunction in fields.items():
        for track in tracks:
             fieldFunction(object, maxX = 10, gradient = 2)

In this example, getConcentration would work, but getFrames would say maxX is an unexpected keyword.

*I edited my post to include my actual minimalist code, as was suggested.

Answer 1

A much better way to avoid all of this trouble is to use the following paradigm:

def func(obj, **kwargs):
    return obj + kwargs.get(a, 0) + kwargs.get(b,0)

This makes use of the fact that kwargs is a dictionary consisting of the passed arguments and their values and get() performs lookup and returns a default value if the key does not exist.

Always access your named arguments through the dictionary kwargs . This makes your life much simpler.

Answer 2

I would go about this by creating a function like the one below with the second parameter optional.

func (obj, a = 0, b = 0):
    return obj + a + b