input: Write a function to create a Python regular expression that matches all numeric strings. The function should print "String is a valid numeric string" if the input string matches the pattern, otherwise it should print "String isn't a valid numeric string". The function should be named match_numeric_string and should take a single argument, the input 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('') == "String isn't a valid numeric string"
  assert match_numeric_string('0') == "String is a valid numeric string"
  assert match_numeric_string('123.456') == "String isn't a valid numeric string"
output: import re
  
  def match_numeric_string(input_string):
      if re.fullmatch(r'\d+', input_string):
          return "String is a valid numeric string"
      else:
          return "String isn't a valid numeric string"