input: Write a python function to check if a string contains special characters.
  assert has_special_characters("HelloWorld") == False
  assert has_special_characters("Hello@World!") == True
  assert has_special_characters("1234567890") == False
  assert has_special_characters("Hello World") == True
output: def has_special_characters(s):
      import re
      return bool(re.search(r'[^\w\s]', s))