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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def export_users(self, format='json'):
 """ Export the users of the Project Notes ----- Each user will have the following keys: * ``'firstname'`` : User's first name * ``'lastname'`` : User's last name * ``'email'`` : Email address * ``'username'`` : User's username * ``'expiration'`` : Project access expiration date * ``'data_access_group'`` : data access group ID * ``'data_export'`` : (0=no access, 2=De-Identified, 1=Full Data Set) * ``'forms'`` : a list of dicts with a single key as the form name and value is an integer describing that user's form rights, where: 0=no access, 1=view records/responses and edit records (survey responses are read-only), 2=read only, and 3=edit survey responses, Parameters format : (``'json'``), ``'csv'``, ``'xml'`` response return format Returns ------- users: list, str list of users dicts when ``'format'='json'``, otherwise a string """

        pl = self.__basepl(content='user', format=format)
        return self._call_api(pl, 'exp_user')[0]