input: from typing import List
  
  def match_numeric_strings(string: str) -> bool:
      """Returns True if the input string is a valid numeric string, False otherwise.
      A valid numeric string consists of digits only.
      >>> match_numeric_strings('123456789')
      True
      >>> match_numeric_strings('abc123')
      False
      """
      import re
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
output:     return string.isdigit()