This is a program that swaps two stack contents using third stack.

stack_swap.py

n = 10

# stack data
class t_stack:
  arr = 0;
  top = 0;
  def __init__(self):
    self.arr = [];

def push(S, value):
  assert(S.top != len(S.arr));
  S.arr[S.top] = value;
  S.top += 1;

def pop(S):
  assert(S.top != 0);
  S.top -= 1;
  result = S.arr[S.top];
  S.arr[S.top] = '0';
  return result;

def move(_from, _to, n=1):
  for i in range(n):
    push(_to, pop(_from));

# initial data
import string;
A = t_stack();
B = t_stack();
C = t_stack();

for i in range(n):
  A.arr.append(string.ascii_lowercase[i]);
  B.arr.append(string.ascii_uppercase[i]);
  C.arr.append('0');
A.top = n;
B.top = n;
C.top = 0;

print(''.join(A.arr));
print(''.join(B.arr));
print(''.join(C.arr));

# move 
move(B, C, n);
move(A, B, n);
move(C, A, n-1);

for m in range(n-1, 1, -1):
  move(B, A, 1);
  move(B, C, m);
  move(A, B, 1);
  move(C, B, m);
move(C, A, 1);

print();
print(''.join(A.arr));
print(''.join(B.arr));
print(''.join(C.arr));