input: def is_numeric_string(string: str) -> bool:
      """ Check if a given string is a valid numeric string using regular expression.
      >>> is_numeric_string('123456789')
      True
      >>> is_numeric_string('abc123')
      False
      """
      import re
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return result is not None
output:     import re
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return result is not None