python 类初始化器中的可选参数

Question

I was wondering if anyone had any good ways of quickly explaining how to efficiently and pythonically create user defined objects with optional arguments. For instance, I want to create this object:

class Object:
    def __init__(self, some_other_object, i, *j, *k):
        self.some_other_object = some_other_object
        self.i = i
        # If j is specified, assume it is = i
        if(j==None):
            self.j = i
        else:
            self.j = j
        # If k is given, assume 0
        if(k==None):
            self.k = 0
        else:
            self.k = k

Is there a better way to do this?

EDIT: I changed the code so that it is more broad and more easily understood.

Answer 1

You can set default parameters:

class OpticalTransition(object):
    def __init__(self, chemical, i, j=None, k=0):
        self.chemical = chemical
        self.i = i
        self.k = k
        self.j = j if j is not None else i

If you don't explicitly call the class with j and k , your instance will use the defaults you defined in the init parameters. So when you create an instance of this object, you can use all four parameters as normal: OpticalTransition('sodium', 5, 100, 27)

Or you can omit the parameters with defaults with OpticalTransition('sodium', 5) , which would be interpreted as OpticalTransition('sodium', 5, None, 0)

You can use some default values but not all of them as well, by referencing the name of the parameter: OpticalTransition('sodium', 5, k=27) uses j 's default but not k 's.

Python won't allow you to do j=i as a default parameter ( i isn't an existing object that the class definition can see), so the self.j line handles this with an if statement that in effect does the same thing.

Answer 2

I am too new to stackoverflow to up-vote or comment, but I approve of ronak's answer. Gareth Latty's comment about default parameters is addressed by using the [default] option of the get method.

dictionary.get(key[, default])

using **args allows for less/ more readable code when there are many optional variables to be passed. It is simply passing passing dictionary key-value pairs as parameters.

Answer 3

You could pass in the args as a dict object and parse through the dict to get whatever you want. If it is not passed, get function will return None and you could check the existence like that.

class Optioncal_transition(object):
  def __init(self, **args):
    self.chemical = args.get('chemical')
    self.i = args.get('i')
    self.j = args.get('j', self.i)

By default, the get function will return None . So if the value exists for j , that will be assigned to self.j otherwise it will be assigned the same value as i