Why is it necessary to use new to initialize an object?

Question

I'm trying to make a game in Python using pygame, but I accidentally had disabled the error checking in PyCharm. As a result, this is how I tried to initialize a Vector2:

self.vel = pg.Vector2(0, 0)
self.acc = pg.Vector2(0, self.GRAVITY)

After I re-enabled the error checking, PyCharm gave me an error message, telling me to use pg.Vector2.__new__(0, 0) instead. After I did, the error message disappeared and the code worked.

Now for the actual question:

While the error messages were disabled, I wrote a lot of bad code like the example above. Strange enough, the code actually ran fine. The game could init and run properly, even while half the code had errors.

Could someone explain to me why the example above works, yet why it is considered bad?

Full code:

import pygame as pg
from game.settings import *


class Player(pg.sprite.Sprite):
    """
    I'm a docstring hurr durr
    """

    ACCELERATION = 60 / FPS  # dummy value
    FRICTION = 1  # dummy value
    GRAVITY = 1  # dummy value
    LIFE = 5

    def __init__(self, x, y, h, w):
        super().__init__()

        self.x = x  # x position
        self.y = y  # y position
        self.h = h  # height
        self.w = w  # width

        self.vel = pg.Vector2.__new__(0, 0)
        self.acc = pg.Vector2.__new__(0, self.GRAVITY)

        self.rect = pg.Rect(x, y, w, h)

        self.image = pg.Surface(w, h)
        self.image.fill(RED)
        # self.image = pg.image.load("../resources/player.*")

    def update(self):
        # key updates
        keys = pg.key.get_pressed()
        if keys[pg.K_LEFT]:
            self.acc.x -= self.a
        if keys[pg.K_RIGHT]:
            self.acc.x += self.a
        # test jumping function
        if keys[pg.K_SPACE]:
            self.vel.y = -20

        # friction
        self.acc.x -= self.vel.x * self.FRICTION

        # update vel and pos
        self.vel.x += self.acc.x
        self.x += self.vel.x

        self.vel.y += self.acc.y
        self.y += self.vel.y

Can we see a bit more context, please? Where *are* those 2 lines of code you posted? Is that in an `__init__` method? Or in a `__new__` method? Can we have a [mcve]? — Aran-Fey, Oct 26 '18 at 10:26
Sounds wrong to use `__new__` explicitly in this case. What exactly is PyCharms warning message? And what version of PyCharm do you use (and also which plugins)? — MSeifert, Oct 26 '18 at 10:33
In general, _new__ and __init__ are discussed in the following thread: https://stackoverflow.com/questions/674304/why-is-init-always-called-after-new — dheinz, Oct 26 '18 at 10:44
Unexpected argument(s) Possible callees: Vector2(self: Vector2) Vector2.__new__(*args, **kwargs) — Jaïr Paalman, Oct 26 '18 at 10:50

score 4 · Accepted Answer · edited Sep 08 '21 at 04:15

The problem here is that PyCharm doesn't know what the real signature of the __init__ method should be, because the file is distributed as a .pyd file (like a .dll). You can verify this by using the "Go to... Declaration" (Ctrl+B) function in pycharm on pg.Vector2 in your code, and then on pygame.math.Vector2 in pygame's __init__.py until you reach the code of pygame.math. Here you'll see a declaration like this:

def __init__(self): # real signature unknown; restored from __doc__
    pass

Observe also the note at the top of this math.py file:

# from C:\Users\User\AppData\Local\Programs\Python\Python35\lib\site-packages\pygame\math.cp35-win_amd64.pyd
# by generator 1.145

PyCharm is doing its best to try and generate something that looks like the actual code, but it is just a guess.

In short, you are right and pycharm is wrong in this case.

The exact same type of problem is described here:

Why do some built-in Python functions only have pass?

Why is it necessary to use __new__ to initialize an object?

1 Answers1

Why is it necessary to use new to initialize an object?