How to define a variable in an init function with a class method?

Question

class TextToNumbers():
    def __init__(self, number):
        self.text = str(number)
        self.chunks = parse_text_to_chunks(self.text)

    def parse_text_to_chunks(text_to_parse):
        #stuff

This is an example of a class I'm building. I want it to define some variables with class methods on initialization. (at least I think that is what I want) I think if I talk about my end goal it is that I have a set of complex information that needs to be available about a class directly at initialization. How do I call a class method at initialization, to define a class variable?

Why do you want to do that? If you initialize a class variable in __init__, what is the point in doing that? — thefourtheye
– thefourtheye, Commented Feb 20, 2014 at 2:40
Not sure. I don't want to have to later tell it to figure it out. Would there be a better way to make that happen? for instance, following the example above, I don't want to have to later say object.parse_text_to_chunks I just want it to do it itself automatically and assign that value to a variable. — Borromakot
– Borromakot, Commented Feb 20, 2014 at 2:44
as @BrenBarn just pointed out it looks like apparently I CAN do it, I just had some silly wrong syntax issue. — Borromakot
– Borromakot, Commented Feb 20, 2014 at 2:46

thefourtheye · Accepted Answer · 2014-02-20 02:43:25Z

2

If you are looking for a way to call an instance method during initialization, you can use self to call that like this

class TextToNumbers():
    def __init__(self, number):
        self.text = str(number)
        self.chunks = self.parse_text_to_chunks(self.text)
        print self.chunks

    def parse_text_to_chunks(self, text_to_parse):
    # 1st parameter passed is the current INSTANCE on which this method is called
        self.var1 = text_to_parse[1:]
        return self.var1

TextToNumbers(123)

And I believe this is what you really need. But if you want a class method

class TextToNumbers():
    def __init__(self, number):
        self.text = str(number)
        self.chunks = TextToNumbers.parse_text_to_chunks(self.text)
        print self.chunks

    @classmethod
    def parse_text_to_chunks(cls, text_to_parse):
    # 1st parameter passed is the current CLASS on which this method is called
        cls.var1 = text_to_parse[1:]
        return cls.var1

TextToNumbers(123)

But there is no point in creating a class method to initialize a class variable in __init__, since a class variable is shared by all the instances of the class, calling from __init__ will overwrite everytime an object is created.

answered Feb 20, 2014 at 2:43

thefourtheye

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6 Comments

Borromakot Over a year ago

So you are saying that because self.chunks is always the same (as it relates to self.text) so I wouldn't want it to be in an init? Where would it belong then?

Borromakot Over a year ago

__init__ variables are unique to each instance of the class, not the same across each class, so wouldn't I want a method in the class, that allows each instance of the class to figure out its own unique variables?

thefourtheye Over a year ago

@Borromakot You are right about the __init__ variables, what I am trying to say is, class variables are not the same as instance variables. The variables created in __init__ with self. are called instance variables.

Borromakot Over a year ago

okay, I think your example got it all worked out for me, and then my inexperience confused the conversation with incorrect vocabulary. Thanks so much!

thefourtheye Over a year ago

@Borromakot No problem :) Enjoy Python :)

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