input: Write a function to create a regular expression in Python to match all numeric strings. The function should take a string as input and return a boolean indicating whether the string is a valid numeric string. If the string is valid, the function should print "String is a valid numeric string"; otherwise, it should print "String isn't a valid numeric string".
  assert check_numeric_string('123456789')==True
  assert check_numeric_string('abc123')==False
  assert check_numeric_string('')==False
  assert check_numeric_string('0.123')==False
  assert check_numeric_string('123 456')==False
output: import re
  
  def check_numeric_string(s):
      if re.fullmatch(r'\d+', s):
          print("String is a valid numeric string")
          return True
      else:
          print("String isn't a valid numeric string")
          return False