python - Django: Class to log a mail error -

i'm trying follow code django unleashed , (by mean often) have problems understand code in full. here exaple of function suppose log errors when mail not sent. part of login system.

    def log_mail_error(self, **kwargs):     msg_list = [         'activation email did not send.\n',         'from_email: {from_email}\n'         'subject: {subject}\n'         'message: {message}\n',     ]     recipient_list = kwargs.get(         'recipient_list', [])     recipient in recipient_list:         msg_list.insert(             1, 'recipient: {r}\n'.format(                 r=recipient))     if 'error' in kwargs:         level = error         error_msg = (             'error: {0.__class__.__name__}\n'             'args: {0.args}\n')         error_info = error_msg.format(             kwargs['error'])         msg_list.insert(1, error_info)     else:         level = critical     msg = ''.join(msg_list).format(**kwargs)     logger.log(level, msg) 

i have hard time 1 part:

error_msg = (             'error: {0.__class__.__name__}\n'             'args: {0.args}\n')         error_info = error_msg.format(             kwargs['error']) 

i don't see 0.class.name comes from. 0 suppose mean? there no object or class called 0 in project. dont understand formatting of error_msg. potentially have 2 fields {} {} fit "kwargs['error']" have 1 value fit 2 places string formatting. agian, why pain {0.__class [...]} if meant placeholder? there going on dont quite understand. can help?

if read format mini language spec you'll notice formatting string can allow passing order of received parameters. example

'{0} , {1}'.format('foo', 'bar') # outputs foo , bar  '{1} , {0}'.format('foo', 'bar') # outputs bar , foo  

this means code specifying parameter used expand format expression should first 1 passed

since actual error object not defined in code, can assume it's of type has args property attached it. in other words, string outputs type of error , parameters built with

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