Python - 将列表作为参数传递给类

Question

So, I have the following code:

locations = [0,1]

class Draw:
    def __init__(self, locations):
        self.locations = locations

    def platforms(self):
        print(self.locations)

Draw.platforms(locations)

And the terminal gives me:

AttributeError: 'list' object has no attribute 'locations'

Is there a specific way to pass a list as an argument? I'm new and I don't understand why it works with a int argument but not with a list.

I want to know why this is happening and what can I do about it.

Thanks in advance.

Answer 1

You're calling the method "platforms" which is not expecting you to pass it a parameter, and are passing it a parameter. The "locations" list is actually passed to the constructor method of your class, which gets called when you instantiate it. Your "platforms" method is called without parameters and prints it.

Here's how you should (probably) do it:

locations = [0,1]

class Draw:
    def __init__(self, locations):
        self.locations = locations

    def platforms(self):
        print(self.locations)

draw = Draw(locations)    
draw.platforms()

Answer 2

What you're doing at the moment is calling platforms([0, 1]) , which then attempts to resolve
[0, 1].locations . That's what your error is telling you: list s don't have locations .

You need to create a Draw object, with a list argument. You can then call the platforms method of that object:

draw = Draw(locations)
draw.platforms()

Answer 3

This could be done with whats called a static method .

locations = [0,1]

class Draw:
    def __init__(self, locations):
        self.locations = locations

    @staticmethod
    def platforms(variable):
        print(variable)

Draw.platforms(locations)

 [0, 1]

Answer 4

locations = [0, 1] class Draw: def __init__(self, locations): self.locations = locations def platforms(self): print(self.locations) Draw(locations).platforms()

Answer 5

I don't understand why it works with a int argument but not with a list.

No, it doesn't:

Traceback (most recent call last):
  File "method.py", line 10, in <module>
    Draw.platforms(locations)
  File "method.py", line 8, in platforms
    print(self.locations)
AttributeError: 'int' object has no attribute 'locations'

The reason why it doesn't work in either case is because you never constructed any instance of your class---you just called on a ("public") method belonging to the class. So when platforms() tries to use self.locations , it doesn't exist.

You could either instantiate the object first:

locations = [0, 1]

drawer = Draw(locations)
drawer.platforms()

Or, if you don't care about keeping the Draw instance around:

locations = [0, 1]

Draw(locations).platforms()

Or you change the method so that it accepts an argument instead:

class Draw:
    def platforms(value):
        print(value)

But now it's basically a static method, and you're only using the class as a namespace.