Its easy enough if you're using the template tags. Just refer to the documentation and you should be set.
First, remember to load the comments tags.
{% load comments %}
To get the number of comments for an object:
{% get_comment_count for entry as comment_count %}
Or quickly display all the comments:
{% render_comment_list for whatever_object %}
If you want more control displaying the comments:
{% get_comment_list for object as comment_list %}
{% for comment in comment_list %}
...
{% endfor %}
However if you're trying to get that info in the code, good luck.
from django.contrib.comments.models import Comment
from django.contrib.sites.models import Site
site = Site.objects.get_current()
comments = Comment.objects.for_model(self).filter(site = site, is_public = True, is_removed = False)
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