input: def match_numeric_strings(string: str) -> bool:
      """ Develop a regular expression in Python to match all numeric strings.
      >>> match_numeric_strings('123456789')
      True
      >>> match_numeric_strings('abc123')
      False
      """
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return result is not None
output:     import re