input: Write a function to develop a regular expression in Python to match all numeric strings. The function should return True if the string is a valid numeric string and False otherwise. If the input string is empty, the function should return False.
  import re
  
  def is_numeric_string(string):
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
  
  assert is_numeric_string('123456789')==True
  assert is_numeric_string('1234a56789')==False
  assert is_numeric_string('0')==True
  assert is_numeric_string('1.23')==False
  assert is_numeric_string('')==False
output: 
  def is_numeric_string(string):
      pattern = '^[0-9]+$'
      result = re.match(pattern, string)
      return bool(result)
  