Python Salute Challenge

salutes.py

def find_all(a_str, sub):
    start = 0
    while True:
        start = a_str.find(sub, start)
        if start == -1: return
        yield start
        start += len(sub) 

def find_salutes(left, right):
  accum = 0
  for l in left:
    for r in right:
      if l < r:
        accum += 1
  return accum * 2


def count_salutes(s):
    leftys = list(find_all(s, '>'))
    rightys = list(find_all(s, '<'))
    if leftys and rightys:
      return find_salutes(leftys, rightys)
    else: return 0


def solution(s):
    return count_salutes(s)


print solution("<<>><")           # 4
print solution(">----<")          # 2
print solution(">---->")          # 0
print solution("--->-><-><-->-")  # 10