为什么在BGE Python中变量不是全局变量

Question

I'm trying to make a simple game in Blender Game Engine using Python controller.

I have a Python controller attached to an Always sensor on a pulse mode and a game property called 'first' on a Sphere, which is also the controlled object.

I want to run a few lines of code only for the first time the game runs, just so it defines the variables and it doesn't overwrite them the next time it runs.

When I run the code below I get an error, that the ForBack and LeftRight variables are not defined. However I can access them from within the if statement.

Am I missing something obvious or what? Also let me know if I could compact this code.

import bge
from bge import logic

cont = bge.logic.getCurrentController()
player = cont.owner
keyboard = bge.logic.keyboard
scene = logic.getCurrentScene()
objs = scene.objects
ACTIVE = bge.logic.KX_INPUT_ACTIVE
first = objs['Sphere']['first']

if(first == True):
    ForBack = 0.0
    LeftRight = 0.0
    print('1')
    print(ForBack)
    objs['Sphere']['first'] = False

if (keyboard.events[bge.events.WKEY] == ACTIVE and ForBack < 50):
    ForBack += 5
    #forward   
if (keyboard.events[bge.events.SKEY] == ACTIVE and ForBack > -50):
    ForBack -= 5
    #backward
if (keyboard.events[bge.events.AKEY] == ACTIVE and LeftRight < 50):        
    LeftRight += 5
    #left
if (keyboard.events[bge.events.DKEY] == ACTIVE and LeftRight > -50):
    LeftRight -=5
    #right

player.applyTorque((ForBack, LeftRight, 0), False)

Answer 1

They are only defined if your first if statement evaluates to True . You access every time in all your if statements which are evaluated each time and in player.applyTorque((ForBack, LeftRight, 0), False) .

You should set the initial value for both outside the first if statement.

ForBack = 0.0
LeftRight = 0.0

if first: 
   ........

What is happening is pretty clear:

if(first == True): # evaluates to false first time
    ForBack = 0.0
    LeftRight = 0.0
    print('1')
    print(ForBack)
    objs['Sphere']['first'] = False

# then you get here and ForBack is not defined
if (keyboard.events[bge.events.WKEY] == ACTIVE and ForBack < 50):
                                                    ^^^^^^

If you only want the others evaluate if the initial if statement is True you need to nest the if's inside the initial if.

if first == True:
    ForBack = 0.0
    LeftRight = 0.0
    print('1')
    print(ForBack)
    objs['Sphere']['first'] = False

    if (keyboard.events[bge.events.WKEY] == ACTIVE and ForBack < 50):
        ForBack += 5
        #forward   
    if (keyboard.events[bge.events.SKEY] == ACTIVE and ForBack > -50):
        ForBack -= 5
        #backward
    if (keyboard.events[bge.events.AKEY] == ACTIVE and LeftRight < 50):        
        LeftRight += 5
        #left
    if (keyboard.events[bge.events.DKEY] == ACTIVE and LeftRight > -50):
        LeftRight -=5
        #right

    player.applyTorque((ForBack, LeftRight, 0), False)