python明确不传递可选参数

Question

设想以下场景:

class A:
    def __init__(self, arg1=3, arg2=5):
        pass

def createA(arg1=None, arg2=None):
    if arg1 is None:
        if arg2 is None:
            a = A()
        else:
            a = A(arg2=arg2)
    else:
        if arg2 is None:
            a = A(arg1=arg1)
        else:
            a = A(arg1=arg1, arg2=arg2)
    return a

实现此行为的最佳方式是什么，请牢记以下几点:

• 我不能/不想更改类 A
• 我不想显式地将 A 的构造函数参数的默认值添加到 createA 函数中？

例如，是否有任何值表示未传递可选参数？像这样的东西:

if arg1 is None:
    newArg1 = NotPassed
else:
    newArg1 = arg1

if arg2 is None:
    newArg2 = NotPassed
else:
    newArg2 = arg2
A(arg1=newArg1, arg2=newArg2)

Answer 1

def create_A(arg1=None, arg2=None):
    kwargs = {}
    if arg1 is not None: kwargs['arg1'] = arg1
    if arg1 is not None: kwargs['arg2'] = arg2
    return A(**kwargs)

甚至可能

def create_A(**kwargs):
    return A(**kwargs)