如何处理python __init__中缺少的参数？

Question

In a multi-threaded implementation, i need to generate lots of instructions, then pass them to the single processing thread. Here is my custom Instruction class:

class instruction:
    priority = 10
    action = ""
    data = ""
    condition = ""
    target = ""

    ### constructor(s) declaration
    def __init__(self,priority=10,target="",action="",data="",condition=""):
        self.priority = priority
        self.target = target
        self.action = action
        self.data = data
        self.condition = condition

I will have to call different kinds of instructions, thus the defined parameters may differ. It will always be one parameter missing, like no target, no action, etc.

As is the current constructor, if i call it without target, i'll get that:

i = instruction(priority_value,action_value,data_value,condition_value)
print(i.priority)
>>> priority_value
print(i.target)
>>> action_value
print(i.action)
>>> data_value
print(i.target)
>>> data_value
print(i.data)
>>> condition_value
print(i.condition)
>>> #nothing to see here, move along!

I know i can define custom constructors, like

@classmethod
def noTarget(priority=10,action=0,data="",condition=""):
return instruction(priority,"",action,data,condition)

and then call it as i=instruction.noTarget(priority_value,action_value,data_value,condition_value)

But, is there other ways to do that?
If so, could you please detail these? Thanks!

Sorry if i mis-used or mis-spelled some words, English isn't my native language.

Answer 1

All your parameters in your function definition are optional as they are specified as default parameters, so you don't have to pass in values for all.

When calling the function, just name the arguments you do want to pass in; these are called keyword arguments:

instruction(priority=priority_value, action=action_value,
            data=data_value, condition=condition_value)

When using keyword arguments in a call, the order doesn't matter, you can mix them up freely.

Also see the Keyword Arguments section of the Python tutorial.

Answer 2

Pass keyword arguments.

i = instruction(priority=priority_value,
                action=action_value,
                data=data_value,
                condition=condition_value)