What is the alphanumeric id in a reddit URL?

Question

What is the 7n5lu in the reddit URL

http://www.reddit.com/r/reddit.com/comments/7n5lu/man_can_fly_if_you_watch_one_video_in_2

...and how is it generated?

Update: @Gerald, I initially thought this is some obfuscation of the id. It is just doing the conversion from integer to a more compact representation. I am thinking, why is this being done? why not use the original integer itself!!

>>> to36(4000)
'334'
>>> to36(4001)
'335'

Answer 1

The reddit source code is available! Here is what I found for generating that string:

def to_base(q, alphabet):
    if q < 0: raise ValueError, "must supply a positive integer"
    l = len(alphabet)
    converted = []
    while q != 0:
        q, r = divmod(q, l)
        converted.insert(0, alphabet[r])
    return "".join(converted) or '0'

def to36(q):
    return to_base(q, '0123456789abcdefghijklmnopqrstuvwxyz')

and elsewhere, under the "Link" class:

@property
def _id36(self):
    return to36(self._id)

Answer 2

That looks like a unique id for the thread. It's most likely used to find the thread in the database.

Answer 3

It is an integer, just in base 36. The id is generated sequentially. For example, the comment right after id 89 is id 8a, etc. Given this, you don't need any other information from the URL.

Comments, posts, messages, users, and subreddits can in theory have the same ID and count up. You can differentiate them by their "fullname" which is the type of thing, an underscore, and then an underscore.

t1 is a comment, t2 is a user, t3 is a submission, t4 is a message, t5 is a subreddit, t6 is an award, ModAction is a moderator action, ModmailConversation is a modmail conversation, etc.

See the API documentation for more information.

Answer 4

Little remark.

It is not sufficient for this example but usually appending to lists

a = []
for i in range(NNN): a.append(i)
a.reverse()

really more efficient than inserting at head.

a = []
for i in range(NNN): a.insert(0,i)

.