code: def common_prefix(s1, s2):
      "Return prefix common of 2 strings"
      if not s1 or not s2:
          return ""
      k = 0
      while s1[k] == s2[k]:
          k = k + 1
          if k >= len(s1) or k >= len(s2):
              return s1[0:k]
      return s1[0:kf common_prefix(s1, s2):
      "Return prefix common of 2 strings"
      if not s1 or not s2:
          return ""
      k = 0
      while s1[k] == s2[k]:
          k = k + 1
          if k >= len(s1) or k >= len(s2):
              return s1[0:k]
      return s1[0:k]
docs: Return prefix common of 2 strings