Is there a more elegant way to add conditional dict elements

Question

Take the following code for instance:

def facebook_sync_album(album_id, thumbnails_only=False):
    args = {'fields':'id,images,source'}
    if thumbnails_only:
        args['limit'] = ALBUM_THUMBNAIL_LIMIT
    response = facebook_graph_query(album_id, 'photos', args=args)

Instead I was wondering if something similar to the following is possible:

def facebook_sync_album(album_id, thumbnails_only=False):
    photo_limit_arg = {'limit': ALBUM_THUMBNAIL_LIMIT}  if thumbnails_only else None
    response = facebook_graph_query_by_user_profile(album_id, 'photos', args={'fields':'id,images,source', photo_limit_arg})

So instead needing to predefine args in order to add an optional element (limit) I could instead pass a variable which expands to a value:key. Somewhat similar to the way you can expand a dict to kwargs using `kwargs

Is this possible?

Is your `args = {'fields':'id,images,source', photo_limit_arg}` in the 1st code block really a `args = {'fields':'id,images,source'}`? The `, photo_limit_arg` part doesn't make sense here. — glglgl, Jan 17 '13 at 08:34

Thorsten Kranz · Answer 1 · 2013-01-17T08:37:03.810

1

You're searching for the .update()-method of Python's dict. You could do:

def facebook_sync_album(album_id, thumbnails_only=False):
    args = {'fields':'id,images,source'}
    args.update({'limit': ALBUM_THUMBNAIL_LIMIT}  if thumbnails_only else {})
    response = facebook_graph_query_by_user_profile(album_id, 'photos', args=args)

Edit

The +-operator for dictionaries, as suggested in the comments, could be like:

class MyDict(dict):
    def __add__(self, other):
        if not isinstance(other, dict):
            return super(MyDict, self).__add__(other)
        return MyDict(self, **other)

    def __iadd__(self, other):
        if not isinstance(other, dict):
            return super(MyDict, self).__iadd__(other)
        self.update(other)
        return self

if __name__ == "__main__":
    print MyDict({"a":5, "b":3}) + MyDict({"c":5, "d":3})
    print MyDict({"a":5, "b":3}) + MyDict({"a":3})

    md = MyDict({"a":5, "b":3})
    md += MyDict({"a":7, "c":6})
    print md

edited Jan 17 '13 at 08:37

answered Jan 17 '13 at 07:30

Thorsten Kranz

12,492
2
39
56

This is no cleaner than the original. It'd be nice to have a builtin that works like + does for lists (which copies one and then calls update and returns the result), but alas there isn't one. – Danica Jan 17 '13 at 07:36
I like this, however eventually I got there with `dict(dict1, **dict2)`. Thanks! – DanH Jan 17 '13 at 07:41
1

For `+`: You could create your own dict-class, inheriting `dict`. It's fun, indeed (see my edit). – Thorsten Kranz Jan 17 '13 at 07:51
This is pretty interesting. Currently though I only have a single use case for this question, however this is a nice snippet. – DanH Jan 17 '13 at 07:56
1

Was only meant *just for fun*. In most cases, this will be an overkill. I always prefer using the basic container types. This makes your code more readable. Everybody who ever worked with C#, especially in a WCF-environment, nows what I'm talking about. – Thorsten Kranz Jan 17 '13 at 07:58
2

Thanks for your feedback. I added this to my sample. – Thorsten Kranz Jan 17 '13 at 08:37

score 0 · Answer 2 · edited May 23 '17 at 11:56

0

Finally came up with the following thanks to https://stackoverflow.com/a/1552420/698289

def facebook_sync_album(album_id, thumbnails_only=False):
    photo_limit_arg = {'limit': ALBUM_THUMBNAIL_LIMIT}  if thumbnails_only else {}
    response = facebook_graph_query_by_user_profile(album_id, 'photos', args=dict({'fields':'id,images,source'}, **photo_limit_arg))

edited May 23 '17 at 11:56

Community

1
1

answered Jan 17 '13 at 07:40

DanH

5,498
4
49
72

Is there a more elegant way to add conditional dict elements

2 Answers2