CODEWITHSUNDEEP
pythonfunction
jonathan topf
jonathan topf

Reputation: 8367

where should I define functions that i use in __init__

I'm writing a class that makes use of some functions inside its __init__ function and I'm not sure about the best practice of where to define those functions. I usually like to define __init__ first but if I need to use the a function/method within the __init__ then it needs to be defined first. I dont want to define it outside the class as its useless outside the class but it seems messy to me to define methods before the __init__. What are the normal conventions for this?

Upvotes: 12

Views: 14451

Answers (4)

Pierre GM
Pierre GM

Reputation: 20339

Why should it be 'messy' to define methods after the init ? Think about it that way :

When you define

class MyClass(object):

    def __init__(self):
        self.something = whatever
        self.do_something_else()

    def do_something_else(self):
        ...

__init__ is a method of your MyClass class, just like do_something is; it's just the first method of the class that will be called when you create an instance of MyClass. So, putting __init__ first is not only customary but also logical.

Your do_something_else method doesn't have to be defined first because you use it in __init__. From the point of view of MyClass, it's a method like another. When you create your myclass=MyClass() instance, do_something_else has already been defined...

Upvotes: 0

MostafaR
MostafaR

Reputation: 3695

It's better to define __init__ function as first function, and you can call functions defined after __init__ inside it.

class A:
    def __init__(self):
        print self.x()

    def x(self):
        return 10

Upvotes: 2

Ghopper21
Ghopper21

Reputation: 10477

The normal convention is indeed to put __init__ before other methods. The reason this works is that functions aren't evaluated until invoked. From the Python docs:

A function definition is an executable statement. Its execution binds the function name in the current local namespace to a function object (a wrapper around the executable code for the function). This function object contains a reference to the current global namespace as the global namespace to be used when the function is called.

The function definition does not execute the function body; this gets executed only when the function is called.

Upvotes: 4

sloth
sloth

Reputation: 101052

Just add the methods to your class like every other method

class Test(object):
    def __init__(self):
        self.hi()

    def hi(self):
        print "Hi!"

No problem at all.

While it is not mentioned in the Python Style Guide IIRC, it's convention to let __init__ be the first method in your class.

Upvotes: 19

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