Python declare object functions at Init

Question

Suppose I have a Class that's passed a set of options.

For example:

class Thing(object): 
    def __init__(self, options): 
        self.name = options['name']
        if options['material'] == 'organic': 
            self.living = options['living'] 
            if self.living: 
                self.kingdom = options['kingdom'] 
        else:
            self.material = options['material']

So if it's material and organic, it will have an additional option specifying if it's living, if it's living it will also have a kingdom etc.

Suppose I want to define a function in class Thing that will for example:

def belongToKingdom(self): 
    print self.kingdom

But I only want such a function defined at __init__ if kingdom is passed in options, otherwise ignored. What's the correct way to accomplish this ?

Yeah I know, it was just supposed to be a simplified example, the actual use case is a little different because there is a set of functions that's dynamically generated from an array of paired values. So I can't just make subclasses for every possible combination of pairs, I actually need to take a standard prototype function and generate it with a few variables determined by the value pairs. — user3467349
– user3467349, Commented Jul 7, 2014 at 8:22

Adam Smith · Accepted Answer · 2014-07-07 08:24:57Z

1

class Thing(object):
    def __init__(self, **options):
        if options.get('living',None):
            def belongToKingdom(self):
                print(self.kingdom)
            self.kingdom = options['kingdom']
            self.belongToKingdom = belongToKingdom

answered Jul 7, 2014 at 8:24

Adam Smith

54.6k13 gold badges84 silver badges120 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

user3467349 Over a year ago

This might be appropriate for a different question, but suppose I don't know what the function I want to define will be called is there a way to str format the function name? I.e. a working equivalent for self.belongTo{0}.format(options['kingdom']) <which would persumably always return True but anyways>

Adam Smith Over a year ago

@user3467349 I can't really make sense of what you're asking, but it sounds like you're trying to put meaningful data in variable names. Don't do that! Just build a list of options instead, so Thing().options returns {'living':True, 'kingdom':"Animal", ... } and test for it

Adam Smith Over a year ago

@user3467349 but of course, there is in fact a way to do just what you want. Instead of manipulating self, manipulate self.__dict__. Then you can use a string instead of a variable name. For example: self.__dict__["belongTo{}".format('kingdom')] = lambda self: print(self.kingdom) works (it's just uglier than sin)

user3467349 Over a year ago

Yes I was just thinking of that. I could also just make a new dictionary right i.e. self.printMyAttribute = {} and then add into it so it looks like {'kingdom': <function kingdom> } etc. Is there a reason you would discourage something like that?

jonrsharpe Over a year ago

@AdamSmith this won't work; belongToKingdom is a function, which isn't quite the same as a method. You need to from types import MethodType then make the assignment self.belongToKingdom = MethodType(belongToKingdom, self)

|

Collectives™ on Stack Overflow

Python declare object functions at Init

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related