input: Write a function to check if a given string is a valid numeric string using a regular expression. If the string is valid return True, else return False. If the given string is empty then return False.
  import re
  
  def is_numeric_string(string):
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      if result:
          return True
      else:
          return False
  
  assert is_numeric_string('123456789')==True
  assert is_numeric_string('123abc456')==False
  assert is_numeric_string('')==False
  assert is_numeric_string('123 456')==False
  assert is_numeric_string('0')==True
output: import re
  
  def is_numeric_string(string):
      if not string:
          return False
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)