Automatically displaying length of list in notebook

Whenever Jeremy displays a list in a notebook cell, it includes the length of the list (which is very handy). For example:

(#421) [Path('bears/black/00000095.jpg'),Path('bears/black/00000133.jpg'),...]

The (#421) is the number of items in the list.

I probably missed this somewhere, but how is this accomplished? Is this a notebook extension, or does fastai monkey-patch the __repr__ of Python lists, or something else?

It is accomplished using a separate data structure known as L which has all the functionalities of Python lists and much more. Check out my article on it here:


Ah, thanks. I saw it mentioned in the lesson or notebooks but didn’t realize it replaced regular lists as well. I’ll check out your article!

EDIT: When I looked at the fastai code earlier, I thought it returned a regular list from get_image_files() but I misread. Now I see it returns an L(...) of that list. That makes sense. :smile:


They’re using L in a lot of places this time :slight_smile: It’s nice

Hi dipam7 hope you’re having a jolly day!

Great post, concise, clear, short and very useful, I hadn’t realized it was so useful!

Cheers mrfabulous1 :grinning: :grinning:

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