input: def match_numeric_strings(string: str) -> bool:
      """ Match a string to see if it's a valid numeric string using regular expression.
      >>> match_numeric_strings('123456789')
      True
      >>> match_numeric_strings('1234abc56789')
      False
      """
      import re
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
output:     import re
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)