Syntax Error in constructor?

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January 6th, 2013, 07:16 PM

Ironbard

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Syntax Error in constructor?

So these past days I've been trying to get back into Python and pygame.

I've settled with Python 3.2 as that's the newest version that pygame supports.

Currently I'm trying to work my way through this tutorial:

Peter Collinridge - Pygame Physics Simulation

[Edit: I'm new so I can't post a hyperlink, but if you google that, it should be the first result]

I've gotten to part 4 without too much trouble - but cannot proceed any further as there is an issue that I don't know how to solve.

I don't think you'll need the whole code, but here it is anyway.

Code:

import pygame
import random
import math

background_colour = (255,255,255)
(width, height) = (300, 200)

class Particle():
    def __init__(self, (x, y), size):
        self.x = x
        self.y = y
        self.size = size
        self.colour = (0, 0, 255)
        self.thickness = 1
        self.speed = 0
        self.angle = 0

    def display(self):
        pygame.draw.circle(screen, self.colour, (int(self.x), int(self.y)), self.size, self.thickness)

    def move(self):
        self.x += math.sin(self.angle) * self.speed
        self.y -= math.cos(self.angle) * self.speed

screen = pygame.display.set_mode((width, height))
pygame.display.set_caption('Tutorial 4')

number_of_particles = 10
my_particles = []

for n in range(number_of_particles):
    size = random.randint(10, 20)
    x = random.randint(size, width-size)
    y = random.randint(size, height-size)

    particle = Particle((x, y), size)
    particle.speed = random.random()
    particle.angle = random.uniform(0, math.pi*2)

    my_particles.append(particle)

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    screen.fill(background_colour)

    for particle in my_particles:
        particle.move()
        particle.display()
    pygame.display.flip()

[Edit: The code should be properly formatted now.]

My problem so far is on line 9:

Code:

def __init__(self, (x, y), size):

I get a syntax error on the inner parenthesis.

Now, I should say that, when last I was familiar with Python, I used v2.x - back then the above code ran fine, so there are a few changes I'll have to adjust to, I know that.

Also I usually don't ask for help, but this thing's got me stumped and all my searches have been in vain.
So, any and all help appreciated - Thanks in Advance.

January 7th, 2013, 01:54 AM

SuperOscar

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Location: Joensuu, Finland

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Quote:

Originally Posted by Ironbard

My problem so far is on line 9:

Code:

def __init__(self, (x, y), size):

I get a syntax error on the inner parenthesis.

Easy enough: change the parameters so that the location is represented by a single tuple, and unpack the tuple:

Code:

def __init__(self, loc, size):
    x, y = loc

If you want to ensure the correctness of parameters, either enclose the unpacking in a try...except block or first check that “loc” is an instance of tuple.

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January 7th, 2013, 06:57 AM

Ironbard

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: D Works like a charm! ^^ So simple, but I have to wonder - why did that change? I mean, when did that change in Python? Why is it necessary to do it like that nowadays?

January 7th, 2013, 09:33 AM

b49P23TIvg

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As I recall, that's a change from python 2 to python 3. You can no longer group tuples of arguments in python3.

They made the change just when I was starting to enjoy the feature. However, you can make assignments like

Code:

$ python3
Python 3.2.3 (default, Oct 19 2012, 19:53:16) 
[GCC 4.7.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(*args):
...  (a,*b,c,) = args  # b gets everything else
...  print('a',a)
...  print('b',b)
...  print('c',c)
... 
>>> f(1,2,3,4,5,6,7)
a 1
b [2, 3, 4, 5, 6]
c 7
>>>

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Syntax Error in constructor?

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