Problem with self.width not being assigned a value

Question

screen_width = 600
screen_height = 600

#Colors
bg = (215, 255, 200)

# game variables cols = columns \\ rows
cols = 6
rows = 6

With the wall class I have self_width = to screen_width // cols. screen_width and cols are both clearly defined variables but when I run my code, I get an error that says:

  line 38, in create_wall
    block_x = col * self.width
AttributeError: 'wall' object has no attribute 'width'"

I have no idea why the two variables aren't executing the math operation and being assigned to self.width so I can create a rect for a pygame.

#brick wall class
class wall():
    def _init_(self):
        self.width = screen_width // cols
        self.height = 50

    def create_wall(self):
        self.block = []
        #define an empty list for an individual block
        block_individual = []
        for row in range(rows):
            #block row list
            block_row = []
            #iterate through each column in that row
            for col in range(cols):
                #generate rectangle based on values
                block_x = col * self.width
                block_y = row * self.height
                rect = pygame.Rect(block_x, block_y, self.width, self.height)