Python不使用int()函数把字符串转换为数字的方法

def atoi(s):
 s = s[::-1]
 num = 0
 for i, v in enumerate(s):
  for j in range(0, 10):
   if v == str(j):
   num += j * (10 ** i)
 return num

def atoi(s):
 s = s[::-1]
 num = 0
 for i, v in enumerate(s):
  offset = ord(v) - ord('0')
  num += offset * (10 ** i)
 return num

def atoi(s):
 s = s[::-1]
 num = 0
 for i, v in enumerate(s):
  t = '%s * 1' % v
  n = eval(t)
  num += n * (10 ** i)
 return num