[NCLUG] help w/ python list comprehension

[Stephen Warren]

On 08/20/2013 07:55 PM, Michael Cullerton wrote:
> Hey Folks,
> 
> This is a bit off topic, but hopefully it's an opportunity (for me) to learn.
> 
> I have the following python code. Is there a way to clean up the chunk inside the "for item in items" loop?
> 
> Mike
> 
> 
> # items is a list of items 
> # filter_tags is a list of tags used to filter the items
> 
> # if an item has all the filter_tags, append it to items_by_tag
> 
> items_by_tag = []
> 
> for item in items:
>     has_tags = True
>     item_tags = [tag for tag in item.tags]

The fact you can use "in" on item.tags here ...

>     for tag in filter_tags:
>         if not tag in item_tags:

... implies you can do so directly there too, and hence avoid even
creating the item_tags variable. In other words, replace that last list
with:

	if not tag in item.tags:


>             has_tags = False

And you may as well add the following here:

		break

> 
>     if has_tags: items_by_tag.append(item)
> 
> return items_by_tag

If you really want to use a list comprehension, e.g. for the sake of
learning them, then perhaps:

items_by_tag = []
for item in items:
	missing = [tag for tag in filter_tags and not tag in item.tags]
	if not missing:
		items_by_tag.append(item)

(note: I hope that list comprehension syntax is correct; I never use
them because they're often considered a little confusing and
unnecessary; just open-coding the loop is a bit more obvious)