code: def add_to(
              self, to_email, global_substitutions=None, is_multiple=False, p=0):
          
  
          if isinstance(to_email, list):
              for email in to_email:
                  if isinstance(email, str):
                      email = To(email, None)
                  if isinstance(email, tuple):
                      email = To(email[0], email[1])
                  self._set_emails(email, global_substitutions, is_multiple, p)
          else:
              if isinstance(to_email, str):
                  to_email = To(to_email, None)
              if isinstance(to_email, tuple):
                  to_email = To(to_email[0], to_email[1])
              if isinstance(to_email, Email):
                  p = to_email.personalization
              self._set_emails(to_email, global_substitutions, is_multiple, p)
docs: Adds a To object to the Personalization object
  
          :param to_emails: A To object
          :type to_emails: To, str, tuple
          :param global_substitutions: A dict of substitutions for all recipients
          :type global_substitutions: dict
          :param is_multiple: Create a new personilization for each recipient
          :type is_multiple: bool
          :param p: p is the Personalization object or Personalization object
                    index
          :type p: Personalization, integer, optional