# Revision history [back]

I edited your code, using string formatting and indentation to get a proper output. More about string formatting see here.

def plusminus(x):
return '+' if x >= 0 else '-'

def calculator(L1,L2,d=0):
# d   -  recursion depth counter, used for indentation
c=0
m=len(L1)
n=len(L2)
if m==0:
pass
elif m==1:
l1=L1[0]
l2=L2[0]
if l1<l2:
c=c+l1
print d*'          '+'c{} = {} '.format(d,c)
else:
for i in range(m):
l1=L1[i]
l2=L2[i]
if l1<l2:
c=c+l2
print d*'          '+'c{} = {} '.format(d,c)
else:
L3 = L1[0:i] + L1[i+1:m]   # in this case list slicing is shorter and more readable
L4 = L2[0:i] + L2[i+1:n]
print d*'          '+'c{} = {} {} calculator({},{})'.format(d,c,plusminus((-1)^m),L3,L4)
c2 = calculator(L3,L4,d+1)
c1 = c  # copy unchanged c for output
c=c+(-1)^m*c2
print d*'          '+'c{} = {} {} {} = {}'.format(d,c1,plusminus((-1)^m),c2,c)
print
return c

#L1=[5,7,3,8]; L2=[7,5,2,6]
L1=[5,7,3]; L2=[7,5,2]
#L1=[5,7]; L2=[7,5]
#L1 = [5]; L2 = [7]
print 'calculator({},{})'.format(L1,L2)
calculator(L1,L2)