Why isn't the direction variable defined

Asked Dec 10 '16 at 20:57

Active Dec 10 '16 at 20:57

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I have a method inside a class that I've written that moves a sprite a set distance towards another instance of the class. However, whenever I call the method, I'm told that - on the 4th line - direction hasn't been defined. This surprised me, as I defined the variable on the line before.

def move_towards(self, sprite, magnitude = 1, anchor = 'center'):
        '''Moves the sprite towards another sprite by a specified magnitude'''
        exec('direction = 360 - atan2(sprite.rect.' + anchor + '[1] - self.rect.centery, sprite.rect.' + anchor + '[0] - self.rect.centerx) * 180 / pi')
        self.rect.x += magnitude * cos(radians(direction))
        self.rect.y -= magnitude * sin(radians(direction))

How do I fix this issue, I've really got no idea how to?

For those wondering, I'm using the exec function as it's the only way I know to use a specific anchor point in the calculation.

asked Dec 10 '16 at 20:57

George Willcox

5

You can't use `exec()` to define new local names. – Martijn Pieters Dec 10 '16 at 20:58
Is there a way I can do what I want without exec? – George Willcox Dec 10 '16 at 20:59
@GeorgeWillcox, of course. Some `if/elif` statements may help – ForceBru Dec 10 '16 at 21:00
@ForceBru so there's no simple way to do it then – George Willcox Dec 10 '16 at 21:01
@GeorgeWillcox: yes, just use `getattr()` to get the `anchor` attribute. `x, y = getattr(sprite.rect, anchor)`, and `direction = 360 - atan2(y - self.rect.centery, x - self.rect.centerx) * 180 / pi`. – Martijn Pieters Dec 10 '16 at 21:01
@GeorgeWillcox, this depends on what you call 'simple' :) – ForceBru Dec 10 '16 at 21:01
Even if you were to do this, which you shouldn't, you'd be using `eval` not `exec`. – kindall Dec 10 '16 at 21:02
@GeorgeWillcox: note that at no point are you actually picking a dynamic *target*, so you could have used `direction = eval(...)`. Not that you need it just to get a dynamic attribute. – Martijn Pieters Dec 10 '16 at 21:04

Why isn't the direction variable defined

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