input: def match_numeric_strings(string: str) -> bool:
      """
      Matches a given string against a regular expression to determine if it is a numeric string.
      
      >>> match_numeric_strings('123456789')
      True
      >>> match_numeric_strings('abc123')
      False
      >>> match_numeric_strings('')
      False
      >>> match_numeric_strings('000000000')
      True
      """
      import re
      pattern = '^[0-9]+$'
      return bool(re.match(pattern, string))
output:     import re
      pattern = '^[0-9]+$'
      return bool(re.match(pattern, string))