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class AlphaBetaAgent(MultiAgentSearchAgent):

  def action(self,gamestate):
    self.alpha= -9999
    self.beta = 9999

    def abc(gamestate, depth, alpha, beta):


    def bvc(gamestate, depth, alpha, beta):


   return abc(gamestate, 0, alpha, beta)

I am calling the getAction function which itself calling the abc funct and abc function calling the bvc funct. The functions abc and bvc are working in recursive way. I need to modify the values of alpha and beta as per the situation demands so I made them local. BUt it is not letting me to do that. Error occurs

Error occurs:- global name 'alpha' is not defined

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  • 6
    Please fix your indentation. In Python, it's kind of important. Commented Aug 2, 2010 at 20:56
  • yeah makes it kinda hard to read ;) Commented Aug 2, 2010 at 20:58
  • I suggest rewriting your function so that it actually does something rather than uselessly assigning values to function arguments and trying to return the value of a function that has no return value. Commented Aug 2, 2010 at 21:07
  • Im using these variables but I have not put down the whole code here... Commented Aug 2, 2010 at 21:10
  • -1: "I am calling the getAction function". Yet, there is not getAction method shown in the example code. Commented Aug 3, 2010 at 3:04

4 Answers 4

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3

In Python, global variables must be declared outside of the function. Then, any function can read that variable without any problems, but if a function wants to write to it it has to declare it global. Example:

def fun1():
     print a
def fun2():
     a = 3
def fun3():
     global a
     a = 3
a = 0
fun1() # <- Will work
fun2() # <- Will raise exception
fun3() # <- Will work
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3 Comments

name 'beta' is a function parameter and declared global - a error occurs like this when I apply your method
I'm not sure exactly what your problem is. If you want to use local variables in a function and manipulate them without worrying about global variables, that works fine, normally. I'm not sure quite what you are doing by declaring a function inside of a function. Have you tried classes instead?
there is a class in which a function Getaction is defined and in getAction fnction, i made 2 more functions
2

Use a class. Storing state & behaviour is what classes are for.

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1 Comment

+1: And avoid global variables. They are often a terrible design blunder.
1

If you want functions like abc and bvc to use common variables, you generally want to define an object for them to be methods of, like so:

class ActionState(object):
   def abc(self, gamestate, depth):
       self.alpha = -9999
       self.beta = 9999
   def bvc(self, gamestate, depth):
       self.alpha = -9999
       self.beta = 99999

def action(self, gamestate):
   state = ActionState()
   state.abc(gamestate, 0)

Alternatively, if you really want to, you can enclose a mutable object like a dict around to hold your data:

def action(self, gamestate):
    actionstate = { 'alpha': 0, 'beta': 0 }

    def abc(gamestate, depth):
        actionstate['alpha'] = -9999
        actionstate['beta'] = 9999

    def bvc(gamestate, depth):
        actionstate['alpha'] = -9999
        actionstate['beta'] = 9999

    abc(gamestate, 0)

Note that the actionstate parameter isn't passed here -- it's inherited from the enclosing scope. You can pass it explicity instead if you want, in which case abc and bvc no longer need to be defined inside of action. The reason this works and your example doesn't is that Python binds any primitive identifier lexically to the most-local function where it is assigned. So when you assign to alpha in abc, Python defines an alpha as local to abc, not action. I believe the only way to get a closure in Python is not to assign to the enclosed variable within the inner function.

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7 Comments

the abc and bvc functions are defined in the function getAction. So where do I exactly define my alpha and beta....I cant use self.alpha??
alpha and beta must be defined as components of a dictionary or object which is created above the definitions of abc and bvc. That way you can assign to them without creating a second version in a more-local scope. See added explanation at end of answer.
Also, why can't you use self.alpha?
When I use self.alpha and self.beta , error occurs. Im not writing the function def abc(self,gamestate,alpha, beta)- it is def abc(gamestate, depth,alpha , beta)
See my first example code -- if you use an object, you do have to change the method signature of abc and bvc. You add self at the beginning and also drop the alpha and beta parameters, because those are kept inside of self. Then you call abc and bvc as methods instead of functions, so they get their implicit self parameters, as also demonstrated in my example. Note that just because a function has a particular signature in some pseudocode you found somewhere, it doesn't necessarily have to look like that when you write it, as long as the same job gets done!
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0

To use a global variable you have to do something like:

global alpha
alpha = -9999

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1 Comment

No when I put the values of alpha & beta inside the function, then a error occurs like global name"alpha " is not defined. When i declared the alpha and beta outside def abc, then it works fine. I want to use alpha nd beta s local variables.

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