Comment Extraction and Parsing

A common use for Reddit’s API is to extract comments from submissions and use them to perform keyword or phrase analysis.

As always, you need to begin by creating an instance of Reddit:

import asyncpraw

reddit = asyncpraw.Reddit(
    user_agent="Comment Extraction (by /u/USERNAME)",
    client_id="CLIENT_ID",
    client_secret="CLIENT_SECRET",
    username="USERNAME",
    password="PASSWORD",
)

Note

If you are only analyzing public comments, entering a username and password is optional.

In this document, we will detail the process of finding all the comments for a given submission. If you instead want to process all comments on Reddit, or comments belonging to one or more specific subreddits, please see SubredditStream.comments().

Extracting comments with Async PRAW

Assume we want to process the comments for this submission: https://www.reddit.com/r/funny/comments/3g1jfi/buttons/

We first need to obtain a submission object. We can do that either with the entire URL:

url = "https://www.reddit.com/r/funny/comments/3g1jfi/buttons/"
submission = await reddit.submission(url=url)

or with the submission’s ID which comes after comments/ in the URL:

submission = await reddit.submission("3g1jfi")

With a submission object we can then interact with its CommentForest through the submission’s comments attribute. A CommentForest is a list of top-level comments each of which contains a CommentForest of replies.

If we wanted to output only the body of the top-level comments in the thread we could do:

comments = await submission.comments()
for top_level_comment in comments:
    print(top_level_comment.body)

While running this you will most likely encounter the exception AttributeError: 'MoreComments' object has no attribute 'body'. This submission’s comment forest contains a number of MoreComments objects. These objects represent the “load more comments”, and “continue this thread” links encountered on the website. While we could ignore MoreComments in our code, like so:

from asyncpraw.models import MoreComments

comments - await submission.comments()
for top_level_comment in comments:
    if isinstance(top_level_comment, MoreComments):
        continue
    print(top_level_comment.body)

The replace_more method

In the previous snippet, we used isinstance() to check whether the item in the comment list was a MoreComments so that we could ignore it. But there is a better way: the CommentForest object has a method called replace_more(), which replaces or removes MoreComments objects from the forest.

Each replacement requires one network request, and its response may yield additional MoreComments instances. As a result, by default, replace_more() only replaces at most 32 MoreComments instances – all other instances are simply removed. The maximum number of instances to replace can be configured via the limit parameter. Additionally a threshold parameter can be set to only perform replacement of MoreComments instances that represent a minimum number of comments; it defaults to 0, meaning all MoreComments instances will be replaced up to limit.

A limit of 0 simply removes all MoreComments from the forest. The previous snippet can thus be simplified:

comments = await submission.comments()
await comments.replace_more(limit=0)
for top_level_comment in comments:
    print(top_level_comment.body)

Note

Calling replace_more() is destructive. Calling it again on the same submission instance has no effect.

Meanwhile, a limit of None means that all MoreComments objects will be replaced until there are none left, as long as they satisfy the threshold.

comments = await submission.comments()
await comments.replace_more(limit=None)
for top_level_comment in comments:
    print(top_level_comment.body)

Now we are able to successfully iterate over all the top-level comments. What about their replies? We could output all second-level comments like so:

submission.comments.replace_more(limit=None)
for top_level_comment in submission.comments:
    for second_level_comment in top_level_comment.replies:
        print(second_level_comment.body)

However, the comment forest can be arbitrarily deep, so we’ll want a more robust solution. One way to iterate over a tree, or forest, is via a breadth-first traversal using a queue:

comments = await submission.comments()
await comments.replace_more(limit=None)
comment_queue = comments[:]  # Seed with top-level
while comment_queue:
    comment = comment_queue.pop(0)
    print(comment.body)
    comment_queue.extend(comment.replies)

The above code will output all the top-level comments, followed by second-level, third-level, etc. While it is awesome to be able to do your own breadth-first traversals, CommentForest provides a convenience method, list(), which returns a list of comments traversed in the same order as the code above. Thus the above can be rewritten as:

comments = await submission.comments()
comments.replace_more(limit=None)
all_comments = await comments.list()
for comment in all_comments:
    print(comment.body)

You can now properly extract and parse all (or most) of the comments belonging to a single submission. Combine this with submission iteration and you can build some really cool stuff.

Finally, note that the value of submission.num_comments may not match up 100% with the number of comments extracted via Async PRAW. This discrepancy is normal as that count includes deleted, removed, and spam comments.