input: Write a function to compress a given string by replacing all repeating characters with a single instance and its count. If the given string is empty then return an empty string.
  def compress(s): 
      if not s:
          return ""
      
      output = "" 
      count = 1
    
      for i in range(len(s) - 1): 
          if s[i] == s[i + 1]: 
              count += 1
          else: 
              output += str(count) + s[i] 
              count = 1
            
      output += str(count) + s[-1] 
    
      return output
  
  assert compress("aabbbbbbcccc") == "2a6b4c"
  assert compress("a") == "1a"
  assert compress("") == ""
  assert compress("aaabbbcc") == "3a3b2c"
  assert compress("abcabc") == "1a1b1c1a1b1c"
output: def compress(s): 
      if not s:
          return ""
      
      output = "" 
      count = 1
    
      for i in range(len(s) - 1): 
          if s[i] == s[i + 1]: 
              count += 1
          else: 
              output += str(count) + s[i] 
              count = 1
            
      output += str(count) + s[-1] 
    
      return output