input: Write a function to match all numeric strings using a regular expression in Python. If the string matches the pattern of a numeric string, return True else return False.
  assert is_numeric_string("123456789")==True
  assert is_numeric_string("abc123")==False
  assert is_numeric_string("")==False
  assert is_numeric_string("123.45")==False
  assert is_numeric_string("0")==True
output: import re
  
  def is_numeric_string(s):
      return bool(re.fullmatch(r'\d+', s))