Why is my code printing 'None'?

Question

My code can be found here: https://github.com/thekarangoel/HackerNewsAPI/blob/master/hn.py

The test case is this:

from hn import HN

hn = HN()

for story in hn.get_top_stories()[:10]:
    print story.print_story()
    print '*' * 50
    print ''

This prints my output like so:

.....
.....
.....
**************************************************

Rank: 3
Story ID: 6231993
Title: Pipe Dream? 3D-Printed Model of Hyperloop Created
Link: http://news.yahoo.com/pipe-dream-3d-printed-model-hyperloop-created-192033757.html
Domain: yahoo.com
Points: 1
Submitted by: evo_9
Number of comments: 0
Link to comments: http://news.ycombinator.com/item?id=6231993
None
**************************************************

Rank: 4
Story ID: 6231992
Title: What colour are your bits?
Link: http://ansuz.sooke.bc.ca/entry/23
Domain: bc.ca
Points: 1
Submitted by: grey-area
Number of comments: 0
Link to comments: http://news.ycombinator.com/item?id=6231992
None
.....
.....

Notice the None at the end of each print? Why is it there? What's wrong with the code?

Answer 1

Seems likes story.print_story() does not return anything.

If a function does not return, it returns None.

>>> def a():
...     print 1
...
>>> print a()
1
None

Remove print from print story.print_story().

Answer 2

It looks like your print_story doesn't return anything. Just replace print story.print_story() with story.print_story().

Here's an example of what is happening:

>>> def print_story():
...     print "story"
... 
>>> print print_story()
story
None
>>> print_story()
story

Answer 3

All function calls in your code are replaced by the function's return value. All functions return None by default. If you have a return statement in your function, then the value specified in the return statement will be returned instead of None.

In this line:

print story.print_story()

the function call:

story.print_story()

is replaced by the return value of print_story(). The print_story() method does not have a return statement in it, so it returns None by default, giving you this:

print None