When are images actually loaded into memory?

Part 1 (2019)
1

Given code:

src = (ImageList.from_csv(path, 'train_v2.csv', folder='train-jpg', suffix='.jpg')

I noticed this returns an ImageList and if I do src[0].show() it’ll actually show me the image! So, I looked at Image.show() and it seems that it does not actually load the image into memory. It just uses Image.data

    def show(self, ax:plt.Axes=None, figsize:tuple=(3,3), title:Optional[str]=None, hide_axis:bool=True,
              cmap:str=None, y:Any=None, **kwargs):
        "Show image on `ax` with `title`, using `cmap` if single-channel, overlaid with optional `y`"
        cmap = ifnone(cmap, defaults.cmap)
        ax = show_image(self, ax=ax, hide_axis=hide_axis, cmap=cmap, figsize=figsize)
        if y is not None: y.show(ax=ax, **kwargs)
        if title is not None: ax.set_title(title)

Which means it must have been done when I called ImageList.from_csv!

But, I can’t seem to find where the image is loaded even here. So I guess my question is, when is the image actually loaded in from the file system?

2

It’s done when you index into the ItemList (which ImageList inherits from). The one bit you didn’t consider (the [0] if you like). Indexing into the ItemList calls ItemList.__getitem__ method which then calls ItemList.open which is overridden in ImageList to do the actual opening.
If you’re not familiar with these dunder methods (__ being a dunder), or magic methods as they are also called, then checkout a python guide. This one looks to have decent coverage here.