input: def match_numeric_strings(string: str) -> bool:
      """Uses a regular expression to check if a given string is composed entirely of numeric characters.
      
      >>> match_numeric_strings('123456789')
      True
      >>> match_numeric_strings('123abc')
      False
      >>> match_numeric_strings('')
      False
      """
      import re
      
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
output:     if string == '':
          return False