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):
      # 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
  assert compress("aabbbbbbcccc") == "2a6b4c"
  assert compress("aaaaaa") == "6a"
  assert compress("abc") == "1a1b1c"
  assert compress("") == ""
  assert compress("a") == "1a"
output: def compress(s):
      if not s:
          return ""
      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