Python：当变量被类方法调用时，有一个带有对象变量的“NameError”

Question

I am making a program with a grid in it, and I need a 2d array. In the constructor for the Grid object, I initialize 2 variables, a tuple that holds coordinates, and a 2d array of objects. The tuple(Named, selected) works perfectly. The array(named gridArray ) does not work as intended.

When I run the program when the method selectCell is called I get the error "NameError: name 'gridArray' is not defined"

To test it I have turned gridArray into a simple int, and the program gives the same error. I have also called it with the following:

Grid.gridArray This gives the error that Grid array doesn't have a variable named gridArray

self.gridArray The error essentially says self isn't defined.

Code:

class Grid:
    def _init_(self):
        gridArray = 5      #[[cell.Cell() for j in range(9)] for i in range(9)]
        selected = (-1,-1)

    def selectCell(x):
        selected = (int(x[0]/const.CELLSIZE),int(x[1]/const.CELLSIZE))
        print(selected)
        print(gridArray)

print(gridArray) should just print 5 instead, it is just a NameError

Answer 1

You need to refer to the gridArray attribute of a specific instance . This is often done with self , and is necessary to distinguish between class variables, instance variables and local variables:

class Grid:

    # Class variables are defined here. All instances of the class share references to them.

    def __init__(self):
        # Anything prefixed with "self" is an instance variable. There will be one for each instance of Grid.
        # Anything without is a local variable. There will be one for each time the function is called.
        self.gridArray = 5
        self.selected = (-1, -1)

    def selectCell(self, x):
        self.selected = (int(x[0] / const.CELLSIZE),int(x[1] / const.CELLSIZE))
        print(self.selected)
        print(self.gridArray)

Answer 2

Every function in a class needs to parse the self variable for it to reference other variables defined in the instance of the class when it's created. Right now, gridArray is a local variable in your __init__ function. You can read more about classes herehttps://docs.python.org/3.7/tutorial/classes.html#class-objects

You should define gridArray as self.gridArray so that you can use it other places in your class. Be sure to also parse the self variable in every function that belongs to a class like this: def selectCell(self, x): the general format is def <funcname>(self, *args): <code> .

Also, the __init__ function should have 2 underscores before and after.