input: Write a function that implements the StringComparator class as described in the instruction, providing methods to compare two strings for equality, difference, and similarity based on a given threshold. The function should include a method to calculate the edit distance between two strings.
  
  class StringComparator:
  
   def __init__(self, string1, string2):
       self.string1 = string1
       self.string2 = string2
  
   def is_equal(self):
       return self.string1 == self.string2
  
   def is_different(self):
       return self.string1 != self.string2
  
   def is_similar(self, threshold=0.5):
       distance = self.edit_distance(self.string1, self.string2)
       max_length = max(len(self.string1), len(self.string2))
       return distance / max_length < threshold
  
   def edit_distance(self, str1, str2):
       len1, len2 = len(str1), len(str2)
       if len1 == 0:
           return len2
       if len2 == 0:
           return len1
       dp = [[0] * (len2 + 1) for _ in range(len1 + 1)]
       for i in range(len1 + 1):
           for j in range(len2 + 1):
               if i == 0:
                   dp[i][j] = j
               elif j == 0:
                   dp[i][j] = i
               elif str1[i-1] == str2[j-1]:
                   dp[i][j] = dp[i-1][j-1]
               else:
                   dp[i][j] = 1 + min(dp[i-1][j], dp[i][j-1], dp[i-1][j-1])
       return dp[len1][len2]
  
  assert StringComparator("hello", "hello").is_equal() == True
  assert StringComparator("hello", "world").is_different() == True
  assert StringComparator("hello", "hella").is_similar(threshold=0.25) == True
  assert StringComparator("hello", "hella").is_similar(threshold=0.1) == False
  assert StringComparator("kitten", "sitting").is_similar(threshold=0.5) == False
output: 
  class StringComparator:
  
   def __init__(self, string1, string2):
       self.string1 = string1
       self.string2 = string2
  
   def is_equal(self):
       return self.string1 == self.string2
  
   def is_different(self):
       return self.string1 != self.string2
  
   def is_similar(self, threshold=0.5):
       distance = self.edit_distance(self.string1, self.string2)
       max_length = max(len(self.string1), len(self.string2))
       return distance / max_length < threshold
  
   def edit_distance(self, str1, str2):
       len1, len2 = len(str1), len(str2)
       if len1 == 0:
           return len2
       if len2 == 0:
           return len1
       dp = [[0] * (len2 + 1) for _ in range(len1 + 1)]
       for i in range(len1 + 1):
           for j in range(len2 + 1):
               if i == 0:
                   dp[i][j] = j
               elif j == 0:
                   dp[i][j] = i
               elif str1[i-1] == str2[j-1]:
                   dp[i][j] = dp[i-1][j-1]
               else:
                   dp[i][j] = 1 + min(dp[i-1][j], dp[i][j-1], dp[i-1][j-1])
       return dp[len1][len2]
  