input: Write a function to match all numeric strings using regular expressions and print whether the string is a valid numeric string or not. The function should take a string as input and return a message as output. If the string matches the numeric pattern, return "String is a valid numeric string"; otherwise, return "String isn't a valid numeric string".
  assert match_numeric_string('123456789')=='String is a valid numeric string'
  assert match_numeric_string('abc123')=='String isn't a valid numeric string'
  assert match_numeric_string('123abc')=='String isn't a valid numeric string'
  assert match_numeric_string('')=='String isn't a valid numeric string'
  assert match_numeric_string('0')=='String is a valid numeric string'
  assert match_numeric_string('789')=='String is a valid numeric string'
output: import re
  
  def match_numeric_string(s):
      if re.fullmatch(r'\d+', s):
          return "String is a valid numeric string"
      else:
          return "String isn't a valid numeric string"