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 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 Submission object we retrieve the comments and look through them to find those that match our criteria. Comments are stored in the attribute 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 replies to get the list of replies to the comment. Note that this may include MoreComments objects and not just Comment.

>>> forest_comments = submission.comments

As an alternative, we can flatten the comment forest to get a unordered list with the function 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 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 Writing a reddit 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 MoreComments with the Comments they represent. We use the replace_more_comments() method to do this. Let’s use this function to replace all MoreComments with the Comments 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 MoreComments PRAW can replace with a single API call is limited. Replacing all 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.

Getting all recent comments to a subreddit or everywhere

We can get comments made to all subreddits by using 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.

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.

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.

The full program

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)