Python, Django: ValueError: unsupported format character '(' (0x28) at index 3

Question

Can somebody explain to me why this raises a ValueError? (using Python 2.7)

from django.utils.translation import ugettext as _

...

template = _('► %(user)s, random text here @[%(friend_id)s] more random text ◄◄◄'.decode('utf-8')) % {'user': friend_profile.user.first_name, 'friend_id': user.id}

This is the error (sent by celery error email):

  File "/var/www/myapp/apps/app/tasks.py", line 54, in notify_friends_new_invite
    template=_('��� %(user)s, random text here @[%(friend_id)s] more random text ���������'.decode('utf-8')) % {'user': friend_profile.user.first_name, 'friend_id': user.id},
ValueError: unsupported format character '(' (0x28) at index 3

Answer 1

Check your message catalog entry.

The _(...) call replaces your unicode value with one from the message catalog (if available), and it is that message that throws this exception. Swapping the % and the preceding space would do this, for example:

>>> '►% (user)s, random text here @[%(friend_id)s] more random text ◄◄◄'.decode('utf-8') % {'user':u'foo', 'friend_id': u'bar'}
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: unsupported format character '(' (0x28) at index 3