CODEWITHSUNDEEP
pythonfunctionglobal-variables
Milan Rasovic
Milan Rasovic

Reputation: 31

Every time variable is changed,i want certain function to be executed

So when i change variable health im trying to inform user that their health has changed by printing "Your health is %s". Heres how it looks like...

health=5

def start():         
  global health
  health+=2

So I'm wondering is there a way to inform the user with some kind of overarching function that is not within this function start() but outside it so that every time variable health is changed it prints that and that? I'm learning python so dont judge!

Upvotes: 1

Views: 1413

Answers (4)

Artemij Rodionov
Artemij Rodionov

Reputation: 1826

We can create a subtype of int.

class Health(int):
    def __new__(cls, value):
        return int.__new__(cls, value)
    def __iadd__(self, other):
        print(f"+{other} health")
        return self.__class__(self + other)
    def __isub__(self, other):
        print(f"-{other} health")
        return self.__class__(self - other)

This is a bit complicated, but an interesting ability. 

In [1]: h = Health(10)

In [2]: h += 2
+2 health

In [3]: h -= 3
-3 health

In [4]: h
Out[4]: 9

But i prefer the approach of @timgeb

Upvotes: 0

N Chauhan
N Chauhan

Reputation: 3515

I think the easiest way is to define a function somewhere in your code:

health = 5
def main():
    global health
    def change_health(amount):
        health += amount
        print('your health went {} by {}'
              .format('up' if amount > 0 else 'down',
                      abs(amount)))

    change_health(-2)

This function uses the global variable health and changes it. Then as described, it prints out that message. The line 'up' if amount > 0 else 'down' I thought was quite nifty: it results in either up or down being formatted depending if the number is positive or not.

The format string means each {} will be replaced with whatever value is put in the .format() call in their respective positions.

Upvotes: 2

Shyryu
Shyryu

Reputation: 149

health=5

def start():
    new_health= health +2
    print new_health, health

I believe this is what you are looking for. Since the your variable is global it could be changed anywhere in the your programme.So by printing both you can see that your original health does not change.

Upvotes: 0

timgeb
timgeb

Reputation: 78680

We can do better than what you are trying to do by having a Player class with a custom __setattr__ hook.

class Player:
    def __init__(self):
        vars(self)['health'] = 100 # suppress __setattr__

    def __setattr__(self, attr, value):
        if attr == 'health':
            print('health changed to {}'.format(value))
        super().__setattr__(attr, value)

Of course, you can expand this class according to your needs. For example, you could add a name attribute and print '{}'s health changed to {}'.format(self.name, value).

Demo:

>>> p = Player()
>>> p.health
100
>>> p.health += 2
health changed to 102

As a bonus, you now can have multiple players with different health levels at the same time and don't have to manage global variables.

Upvotes: 3

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