Why does my class raise an AttributeError?

Question

I might be blind, but I really can't see why this class fails with:

AttributeError: NextSunday instance has no attribute 'trigger'

from datetime import datetime
from datetime import time
from datetime import timedelta
class NextSunday():
 def __init__(self, trigger=None):
 """
 Get date of, and number of days until, next Sunday.
 Arguments:
 - `trigger`: Add an extra week if less than trigger number of days.
 """
 self.str = u'%s (%s days)' % (self.date().date(), self.no_days())
 self.trigger = trigger
 def __unicode__(self):
 return self.str
 def __str__(self):
 return unicode(self).encode('utf-8')
 def __repr__(self):
 return '<Next Sunday: ' + self.str + '>'
 def no_days(self):
 """Get date of next sunday. """
 days = None
 for i in range(7):
 dt = datetime.now() + timedelta(days=i)
 if dt.weekday() == 6:
 days = i
 # Add another week if there are less days left then trigger
 if self.trigger:
 if days < self.trigger:
 days += 7
 return days
 def date(self):
 # The datetime obj contains the next sunday, but also the current time
 dt_of_next_sun = datetime.now() + timedelta(days=self.no_days())
 # Get the whole day
 date_of_next_sun = datetime.combine(dt_of_next_sun.date(),
 time(23, 59))
 return date_of_next_sun

• Karoly Horvath: eliminiate the unnecessary lines, till you locate the root of the problem.
• Marcin: The full stacktrace would identify the originating line.
• Keith: This is why I developed the habit of always setting instance variables first, at the top of the initializer, before calling any methods.

Answer 1

You need to switch these

 self.str = u'%s (%s days)' % (self.date().date(), self.no_days())
 self.trigger = trigger

like this

 self.trigger = trigger
 self.str = u'%s (%s days)' % (self.date().date(), self.no_days())

because otherwise the no_days method is called before the self.trigger attribute is created. This is bad because the no_days method tries to read the value of the self.trigger attribute:

if self.trigger:
 if days < self.trigger:

• Niclas Nilsson: Oh, that was interesting. It solved the problem (marks the question as solved soon). But why is this? I can't see it.
• Karoly Horvath: you call no_days before trigger is set.
• Lauritz V. Thaulow: @Niclas I've updated my answer with what is hopefully a more thorough explanation.
• Niclas Nilsson: @lazyr Oh, that should be obvious. But I havn't encountered this before so I did'nt think about it. Thanks alot!