Python, confused by dot notation

Question

I'm currently reading Python Crash Course, and there is that code:

import pygame


class Ship():


    def __init__(self, screen):

        """Initialize the ship, and set its starting position."""

        self.screen = screen



        # Load the ship image, and get its rect.

        self.image = pygame.image.load('images/ship.bmp')

        self.rect = self.image.get_rect()

        self.screen_rect = screen.get_rect()


        # Start each new ship at the bottom center of the screen.

        self.rect.centerx = self.screen_rect.centerx

        self.rect.bottom = self.screen_rect.bottom

I'm pretty sure i'm asking basic stuff, but nor my brain, nor my google skills aren't that good.

This thing: self.rect = self.image.get_rect(). Aren't get_rect() part of pygame.Screen module? If so, shouldn't it be used like pygame.Screen.get_rect()?
self.rect.centerx = self.screen_rect.centerx Too.many.dots. Is rect class instance, that is being created by get_rect() method, and centerx is attribute of that instance? Also, screen variable (or class instance?) is defined like that: screen = pygame.display.set_mode((1200, 800))

Thanks in advance!

Edit: Thanks for answers!

This isn't about not good at googling, it's more like not understanding Python's dot notation syntax at all. Would recommend you reading a tutorial first before attempting to understand everything. — Taku
– Taku, Commented Mar 19, 2017 at 22:49
There is nothing to be confused about; the dot always (...except in a float literal like 1.23) means accessing an attribute. The object which has the attribute (hopefully, or you get an AttributeError) is on the left (and can itself be an attribute of another object, as you see in your examples) and the name of the attribute is on the right. +1 for reading a tutorial, see sopython.com/wiki/What_tutorial_should_I_read%3F — jonrsharpe
– jonrsharpe, Commented Mar 19, 2017 at 22:52

meyer9 · Accepted Answer · 2017-03-19 22:54:45Z

2

In PyGame, the get_rect() function is defined in a class that represents some sort of surface. In this case, both the screen and the image have that method because both subclass surfaces and so they both have the get_rect() method.
This code: self.rect.centerx = self.screen_rect.centerx can be translated as setting the centerx of the rect of myself to the centerx of the screen of myself. In other words, it moves the object to the center of the screen. The self keyword represents the current object and each dot represents a property of that object.

answered Mar 19, 2017 at 22:54

meyer9

1,1409 silver badges26 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Lie Ryan · Accepted Answer · 2017-03-19 23:10:29Z

get_rect() is a method of Surface. Both Screen and Image are a Surface (they implement the Surface interface). Screen is just special Surface that refers to the Surface that's actually mapped to a location on-screen, while other Surfaces like Image are off-screen object in the memory that can be drawn or drawn into without affecting what's on the screen.

self.rect is a Rect instance, which is used by pygame to track the position and dimension of Surface/s.

Collectives™ on Stack Overflow

Python, confused by dot notation

2 Answers 2

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Related