input: from typing import Tuple
  
  def longest_common_substring(str1: str, str2: str) -> Tuple[str, int]:
      """ Find the longest common substring between two strings and return the substring along with its length.
      >>> longest_common_substring("Helwallomst", "Welcome")
      ('ello', 4)
      """
      match = 0
      substr = ""
      for i in range(len(str1)):
          for j in range(len(str2)):
              l = 0
              while (i + l < len(str1) and j + l < len(str2) and str1[i + l] == str2[j + l]):
                  l += 1
              if l > match:
                  substr = str1[i:i + l]
                  match = l
      return substr, match
output:     match = 0
      substr = ""
      for i in range(len(str1)):
          for j in range(len(str2)):
              l = 0
              while (i + l < len(str1) and j + l < len(str2) and str1[i + l] == str2[j + l]):
                  l += 1
              if l > match:
                  substr = str1[i:i + l]
                  match = l
      return substr, match