.. _comment_parsing:

Comment Parsing
===============

A common task for many bots and scripts is to parse a submission´s comments. In
this tutorial we will go over how to do that as well as talking about comments
in general. To illustrate the problems, we'll write a small script that replies
to any comment that contains the text "Hello". Our reply will contain the text
" world!".

Submission Comments
-------------------

As usual, we start by importing PRAW and initializing our contact with
reddit.com. We also get a :class:`.Submission` object, where our script will
do its work.

>>> import praw
>>> r = praw.Reddit('Comment Scraper 1.0 by u/_Daimon_ see '
...                 'https://praw.readthedocs.org/en/latest/'
...                 'pages/comment_parsing.html')
>>> submission = r.get_submission(submission_id='11v36o')

After getting the :class:`.Submission` object we retrieve the comments and
look through them to find those that match our criteria. Comments are stored in 
the attribute :attr:`.comments` in a comment forest, with each tree root a
toplevel comment. E.g., the comments are organized just like when you visit the
submission via the website. To get to a lower layer, use :attr:`.replies` to
get the list of replies to the comment. Note that this may include
:class:`.MoreComments` objects and not just :class:`.Comment`.

>>> forest_comments = submission.comments

As an alternative, we can flatten the comment forest to get a unordered list
with the function :func:`praw.helpers.flatten_tree`. This is the easiest way to
iterate through the comments and is preferable when you don't care about
a comment's place in the comment forest. We don't, so this is what we are going
to use.

>>> flat_comments = praw.helpers.flatten_tree(submission.comments)

To find out whether any of those comments contains the text we are looking for,
we simply iterate through the comments.

>>> for comment in flat_comments:
...     if comment.body == "Hello":
...         reply_world(comment)

Our program is going to make comments to a submission. If it has bugs, then it
might flood a submission with replies or post gibberish. This is bad. So we
test the bot in `r/test <http://www.reddit.com/r/test>`_ before we let it loose
on a "real" subreddit. As it happens, our bot as described so far contains a
bug. It doesn't test if we've already replied to a comment before replying. We
fix this bug by storing the content_id of every comment we've replied to and
test for membership of that list before replying. Just like in
:ref:`writing_a_bot`.

The number of comments
----------------------

When we load a submission, the comments for the submission are also loaded, up
to a maximum, just like on the website. At reddit.com, this max is 200
comments. If we want more than the maximum number of comments, then we need
to replace the :class:`.MoreComments` with the :class:`.Comment`\s they represent.
We use the :meth:`.replace_more_comments` method to do this. Let's use this
function to replace all :class:`.MoreComments` with the :class:`.Comment`\s they
represent, so we get all comments in the thread.

>>> submission.replace_more_comments(limit=None, threshold=0)
>>> all_comments = submission.comments

The number of :class:`.MoreComments` PRAW can replace with a single API
call is limited. Replacing all :class:`.MoreComments` in a thread with many
comments will require many API calls and so take a while due to API delay between
each API call as specified in the
`api guidelines <https://github.com/reddit/reddit/wiki/API>`_.

Getting all recent comments to a subreddit or everywhere
--------------------------------------------------------

We can get comments made to all subreddits by using
:meth:`~praw.__init__.UnauthenticatedReddit.get_comments` and setting the
subreddit argument to the value "all".

>>> import praw
>>> r = praw.Reddit('Comment parser example by u/_Daimon_')
>>> all_comments = r.get_comments('all')

The results are equivalent to `/r/all/comments
<http://www.reddit.com/r/all/comments>`_.

We can also choose to only get the comments from a specific subreddit. This is
much simpler than getting all comments made to a reddit and filtering them. It
also reduces the load on the reddit.

>>> subreddit = r.get_subreddit('python')
>>> subreddit_comments = subreddit.get_comments()

The results are equivalent to
`r/python/comments <http://www.reddit.com/r/python/comments>`_.

You can use multi-reddits to get the comments from multiple subreddits.

>>> multi_reddits = r.get_subreddit('python+learnpython')
>>> multi_reddits_comments = multi_reddits.get_comments()

Which is equivalent to `r/python+learnpython/comments
<http://www.reddit.com/r/learnpython+python/comments>`_.

The full program
----------------

.. code-block:: python

    import praw

    r = praw.Reddit('Comment Scraper 1.0 by u/_Daimon_ see '
                    'https://praw.readthedocs.org/en/latest/'
                    'pages/comment_parsing.html')
    r.login('bot_username', 'bot_password')
    submission = r.get_submission(submission_id='11v36o')
    flat_comments = praw.helpers.flatten_tree(submission.comments)
    already_done = set()
    for comment in flat_comments:
        if comment.body == "Hello" and comment.id not in already_done:
            comment.reply(' world!')
            already_done.add(comment.id)
