input: Write a function to compress a given string by replacing all repeating characters with a single instance and its count.
  
  def compress(s): 
      # Initialize results 
      output = "" 
    
      # Initialize count 
      count = 1
    
      # Traverse the string 
      for i in range(len(s)): 
            
          # If the current character is same 
          # as next one, increment its count 
          if (i+1 < len(s) and s[i] == s[i+1]): 
              count += 1
            
          else: 
              # Append the count and character 
              output += str(count) + s[i] 
            
              # Reset the  count  
              count = 1
            
      return output
  
  s = "aabbbbbbcccc"
  print(compress(s))
  # Output: 2a6b4c
output: def compress(s): 
      output = "" 
      count = 1
      for i in range(len(s)): 
          if (i+1 < len(s) and s[i] == s[i+1]): 
              count += 1
          else: 
              output += str(count) + s[i] 
              count = 1
      return output