self is not defined in class method argument

Question

I have 4 classes with several methods in each of them. I need these methods to use some class variables as arguments, eg.

class Orange:
    def __init__(self,banana):
        self.banana = banana

    def apple(self,fruit=self.banana):
        return something

I already found out that this does not work as method arguments are defined when function is created, not when it is called, so i found a workaround here:

def apple(self,fruit=None):
    if fruit is None:
        fruit = self.banana

But the problem is, that i have about 50 arguments (no in each method, but summary from all methods of all classes) and using this method, i would get about one hundred new lines of code and that seems to me like very "dirty" workaround... isnt there any easier way how to reach that?

[Will kwargs help?](https://stackoverflow.com/questions/1769403/understanding-kwargs-in-python) — Madhan Varadhodiyil, Aug 07 '18 at 07:53
Can you please explain what you want to do with your methods? Your example is a bit weird... — toti08, Aug 07 '18 at 07:53
well, you can use a conditional expression: `fruit = self.banana if fruit is None else fruit`. So that cuts your lines in half. I would just use the full statement. — juanpa.arrivillaga, Aug 07 '18 at 07:56
Are you *sure* you need to have a method with 50(!) arguments? — Aran-Fey, Aug 07 '18 at 08:00

Henry Woody · Answer 1 · 2020-07-02T16:22:30.317

There are two ways to go with this problem.

Option 1

Use the method you have shown in your problem statement, but perhaps with a ternary operator to trim the number of lines:

def apple(self, fruit=None):
    fruit = fruit if fruit is not None else self.banana

Option 2

Consider revising the structure of your code. For example, it might not be necessary to allow the fruit used in each method to vary when called, and instead just using a preset option, like self.banana. (Basically just remove the keyword argument fruit altogether and just go ahead and use self.banana instead.) For those that do need to vary when the method is called, then resort to Option 1.

Option 2 is a better approach. If you have 50 arguments you could use *args or **kwargs accordingly — Ravinder Baid, Aug 07 '18 at 08:45

Jan Musil · Accepted Answer · 2019-07-25T08:37:11.380

Thanks guys, thanks to your comments and answers i found a complete solution.

>>> class Orange:
...     def __init__(self,banana="a"):
...         self.banana = banana
...     def apple(self,**kwargs):
...         self.__dict__.update(kwargs)
...         return self.banana
...
>>> test = Orange()
>>> test.apple()
'a'
>>> test.apple(banana="b")
'b'

So as you can see, passing different keyword variable will change the result, exactly as i wanted. However, only disadvantage (but it can be also advantage, depends on point of view) is, that this change is permanent so if we call the function again, its still changed like this:

>>> test.apple()
'b'

But this is not problem for me at all. If anyone wonders how to make this changes only temporary, save original init values to dict, and then when you want to use them, update the class dict, with variable where these values are saved, as following:

>>> class Orange:
...     def __init__(self,fruit={"banana":"a","cherry":"b"}):
...         self.fruit=fruit
...     def apple(self,**kwargs):
...         self.__dict__.update(self.fruit)
...         self.__dict__.update(kwargs)
...         return self.banana
...
>>> test = Orange()
>>> test.apple()
'a'
>>> test.apple(banana="b")
'b'
>>> test.apple()
'a'

Self.fruit stores original information, and it refreshs class variables in the beginning of function. If something is in kwargs, it just overrides it.

score 0 · Answer 3 · answered Jul 02 '20 at 04:01

0

The Best Option is to make separate Mutator for it

def setFruit(self, fruit):
    self.fruit = fruit

answered Jul 02 '20 at 04:01

Muhammad Hazrat

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self is not defined in class method argument

3 Answers3