无法在Python中调用方法

Question

Right now I have a method in my class that's really simple, but I'm have a hard time calling it.

def size(self):
  return self.size

The call I'm required to use is this:

print(str(ll.size()))

Which always leads to this output:

print(str(ll.size()))
TypeError: 'int' object is not callable

I've been told several times it's the way I have the size() method set up, but I've never been able to understand it. Can someone show me the proper way to make a method that can be called like this and explain the difference for future reference? Thanks!

Answer 1

It seems like your class has two attributes called size , one being the method you have defined and one being the property you're calling from inside your method.

From the error message you can tell that the second one is begin called. So, ll.size is an int and ll.size() is 'calling' that int.

Try to rename your method to something else than size and see if that works.

Answer 2

You can't have both a instance variable name size and an instance method name size .

How would one distinguish them ?

Here the instance variable take precedence because it was define first (you probably have a self.size = x in your __init__ method and therefore appearing first in your object __dict__ ) which is a int and therefore not callable.

If you have nothing special to do on the size value just use the attribute directly without defining a function:

class Foo:
        def __init__(self, somearg):
            # ...
            self.size = somearg * 3
>>> foo = Foo(3)
>>> foo.size
9

If you want to make something more complex (contrary to my trivial example here) use a property :

class Foo:
    def __init__(self, somearg):
        # ...
        self._size = None
        self._someattr = somearg
    # ...
    @property
    def size(self):
        if self._someattr > 2:
            return self._someattr * 3
        return 1
>>> foo = Foo(3)
>>> foo.size
9
>>> bar = Foo(2)
>>> bar.size
 1

To fully understand the advantage of the property decorator read this tutorial