Declaring Variables

Game Engine Game Engine Support and Discussion
#1

Hi,
I can’t figure out how to declare variables without assigning them a value.

If i try this:

import bge
cont = bge.logic.getCurrentController()

key = cont.sensors[“Keyboard”]

if key.positive == True:
test += 1

It gives me the error: name “test” is not defined

If i try this:

import bge
cont = bge.logic.getCurrentController()

key = cont.sensors[“Keyboard”]

test = 0
if key.positive == True:
test += 1

It assigns the value 0 to the variable everytime the script is run (every frame)

Then i tried this:

import bge
cont = bge.logic.getCurrentController()
own = cont.owner

key = cont.sensors[“Keyboard”]

if “init” not in own:
test= 0

if key.positive == True:
test += 1

But it gives me the same error.

So, is there a way to declare a variable without assigning to that a value?
Thanks a lot

#2

So, you want to keep a variable in existance between frames?
You’r last example is half way there:


import bge
cont = bge.logic.getCurrentController()
own = cont.owner

key = cont.sensors['Keyboard']

if not 'count' in own:
    own['count'] = 0 

if key.positive:
    own['count']+=1
#3

yes, i knew this method, but if my variable is not an integer but an array or an object?

#4

Same method applies. You can initiate it in the gameobject by using


if not 'x' in object:
    object['x'] = datatype

or, an extension of this:


import bge

class instanceClass:
    def __init__(self):
	    self.x = 1

def main(cont):
	own = cont.owner
    if not 'instance' in own:
	    own['instance'] = instanceClass()
	
	#after the code above, if there isn't a registered class already
	#it will be created on the gameobject.
	
	#now just use the handle (own['instance']) and modify its attribute (in this case x)
	
	print(own['instance'].x) #get the value of x in the instance
	own['instance'].x = 2 #set the value of x in the instance
#5

Wow, thanks a lot agoose :smiley:

#6

So, you want to keep a variable in existance between frames?
You’r last example is half way there:

Is there a similar way to do this with globalDict’s

#7

Yes, there is.


import bge

cont = bge.logic.getCurrentController()
own = cont.owner

if not "my_key" in bge.logic.globalDict:
    bge.logic.globalDict['my_key'] = 0

if cont.sensors[0].positive:
    bge.logic.globalDict['my_key'] += 1

GlobalDict is a dictionary, just like the way you store variables on an object. You can treat them the same :slight_smile:

#8

Just your our clarification:

A variable lives as long as any reference to the variable exist.
If you reference the variable in a function it will live as long as the function is executed. When leaving the function the variable will die.

The script mode is like a function. After leaving the script all variables die. A variable can survive if you keep a reference somewhere else (module, property etc.). The variable will die with the death of the last reference to it.

Example:


foo = ["demo","list"] # birth of foo
print (foo, id(foo) )
foo.pop()
foo.pop() # remove existing values
foo.extend(["list","with","new","values"]) # add new values
print (foo, id(foo) )
foo = ["other","list"] # foo is dead, long lives foo
print (foo, id(foo) )
# the second foo dies here too