python: TypeError: 'long' object is not callable

python: TypeError: 'long' object is not callable

I get this error when trying to convert possible integer variables:
for page in domain.page_set.all():
filename = str(domain.url) + '_page_' +str(page.id())+ '.html'
The error:
File
"/Applications/djangostack-1.4.7-0/apps/django/django_projects/controls/polls/models.py",
line 40, in make_config_file
filename = str(domain.url)+"_page_"+str(page.id())+".html"
TypeError: 'long' object is not callable
What is wrong here? what does "long is not callable" means?