CODEWITHSUNDEEP
pythoninheritance
Justin Eyster
Justin Eyster

Reputation: 1

My classes think that "self" is an argument that needs a value assigned

I'm not sure why this is happening. It seems to think that "self" requires an argument, which doesn't make any sense.

Here's my code:

class Animal:

    def __init__(self):
        self.quality = 1


class Bear(Animal):

    def __init__(self):
        Animal.__init__(self)

    def getImage(self):
        return "bear.ppm"

class Fish(Animal):

    def __init__(self):
        Animal.__init__(self)

    def getImage(self):
        return "fish.ppm"

And the error I get is:

Traceback (most recent call last):

  File "<pyshell#1>", line 1, in <module>
    Bear.getImage()

TypeError: getImage() takes exactly 1 argument (0 given)

Upvotes: 0

Views: 72

Answers (2)

doubleo
doubleo

Reputation: 4759

getImage() is an instance method, so it can only be called with a instantiation of Bear class. So here is how you can do it:

Bear().getImage()

or 

be = Bear()
be.getImage()

Upvotes: 0

dano
dano

Reputation: 94871

You have to instantiate Bear before you call getImage():

b = Bear()
b.getImage()

getImage is an instance method, so it is only designed to be called on a specific instance of the Bear class. The state of that instance is what is passed as the self variable to getImage. Calling b.getImage() is equivalent to this:

b = Bear()
Bear.getImage(b)

So, without an instance of Bear, there is nothing that can be used for the self argument, which is why you see that exception when you called Bear.getImage(). See the documentation on Python instance methods for more information.

If you want to be able to call getImage on the class Bear rather than on a specific instance, you need to make it a static method, using the @staticmethod decorator:

class Bear(Animal):

    def __init__(self):
        Animal.__init__(self)

    @staticmethod
    def getImage():
        return "bear.ppm"

Then you could call Bear.getImage().

Upvotes: 8

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