nested loop list comprehension in python ; can't recognize variable in outer loop

Question

def  maxXor( l,  r):
return max(a^b for b in range(a,r+1) for a in range(l,r+1))

The error shows NameError: global name 'a' is not defined.

I think the error is range(a,r+1)

Here I want the 'a' in range(a,r+1) reference 'a' in the inner loop for a in range(l,r+1)).

You're missing the [square brackets] for the nested list comprehensions. This does the trick: def maxXor( l, r): return max([[a^b for b in range(a,r+1)] for a in range(l,r+1)]) — matiu, Apr 08 '15 at 00:56
@matiu When the list is a para in function, actually the square brackets could be omit. Problem solved by Steven. Also thanks for your help. — AlexWei, Apr 08 '15 at 01:00

score 3 · Accepted Answer · answered Apr 08 '15 at 00:57

3

def  maxXor( l,  r):
    return max(a^b  for a in range(l,r+1) for b in range(a,r+1))

answered Apr 08 '15 at 00:57

Julien Spronck

1 Answers1