[Tutor] Re: variable scope in nested functions: SOLUTION :-)

[André Roberge]

Logesh Pillay wrote:
[snip]
> 
> Consider a program I've just translated into python from my version in C.
> 
> def erdos(n):                                          

      global found       # added line

>    found, r, s = False, 1, [0]*1000            
>    def choose (d, k):      

          global found   # added line

>        for i in -1, 1:                                       
>            s[d] = i
>            if d < r:
>                choose (d+1, k - i*d*d)
>            elif k == i*d*d:
>                found = True
>                printout ()
>    def printout ():
>        print n, '=',
>        for i in range (1, r+1):
>            if s[i] == 1:
>                print '+', i,'.',i,
>            else:
>                print '-',i,'.',i,
>        print '\n'
>    while not found:
>        choose(1, n)
>        r += 1
> 
> The program is supposed to return to the python prompt as soon as it 
> finds solution(s) at the smallest width r.
> 
> I entered it exactly as it is expecting the same sort of error message 
> for the boolean variable 'found'.  There was none.  Instead python 
> simply fails to perform 'found = True' in choose() and it just keeps 
> running (incidentally demonstrating the other part of this Erdos theorem 
> that the no. can be  so  expressed  in an infinite number of ways).  
> Why  the inconsistency  in handling enclosing scope variables of type 
> 'int' and 'bool'?  Also, it can't be desirable that the interpreter 
> effectively ignores a line of code without warning.
> 
> Logesh
> _______________________________________________

Just add two global statements as written above and it will work just as 
you would have expected it to!

André