adaliabooks: Ok, a quick look at the library suggests it wouldn't be trivial to do as the information is only on the second layer (when you click on the game on the shelf) and would require an AJAX call for each game, which would soon probably crash the system if you have over 100 - 200 games...

But there may be other ways to do it.
Have you looked at MaGog? You can import your owned games into it and could then display a list of them, adding them with a script would be far easier that way. Not sure if it's more or less hassle than gogrepo would be though...

timppu: Either way, I suggest you try out gogrepo.py. When you start the actual download of your games/extras with gogrepo, it will tell you right at the start how much exactly is still to be downloaded (total), which is the figure you're after. You can cancel the download right there if your intention was not to download your games but just to see how much space they will take.

Links: Thank you for looking into it.

I was writing before your later replies (and now deleted all of the reply), and tried now with your method. I'm glad you engaged with this puzzle. :)

I'm checking now some specific games, and it seems MaGog has issues with file sizes for some of them, for example The Witcher 3 or the Zork Anthology, but it certainly makes a manual count simpler.

Thank you for confirming this. If it gets too complicated I will go with gogrepo, it really looks like a fine piece of programming in any case.

adaliabooks: [snip]
And in the Options section change Output Format to JSON.
You could output this as HTML and do it manually (it does include all the sizes for the bonuses etc. too), unfortunately the formatting doesn't lend itself to scraping easily.

Otherwise, once on the JSON output page, run this script from your browser's console. It should give you an output in MB of the size of your library.
[snip]

HunchBluntley: MaGog already calculates the total file size of the games in your search results (based on the info on each game's store page) at the bottom of each results page, as well as showing the average file size per game (though I struggle to think of a scenario in which knowing the average file size would be all that useful). Am I misunderstanding? Is this not what your script is also meant to show?

adaliabooks: LOL
Whoops, that is indeed what it does. I rarely reach the bottom of the results page so didn't notice that XD
Trust mrkgnao to be one step ahead...

adaliabooks:

HunchBluntley: I don't suppose the script could be altered to instead total the numbers from the various sub-categories of the "Downloadable Files" category? Then it might still serve an otherwise-unfulfilled purpose to Links. (At least, I don't think MaGog can do that on its own..yet. But she's probably listening...planning....)
EDIT: Closed italics tag and corrected inadvertent reference to MaGog doing carpentry.

HunchBluntley: What fun's an existing solution when a new, more complex one can be dreamt up, eh? =D

adaliabooks: Technically yes, but the issue there is there's no easy way to identify those via javascript. They don't have any unique class (the easiest way to find them) so you'd have to regex it or something.
Then you have to parse whether it's GB or MB (or KB?) and adjust accordingly.
It's certainly doable, but not in the vein of a quickly thrown together script. I'll have another look at it when I can be bothered and make it do a more accurate count.

adaliabooks: Also, yes. Totally XD

These [url=https://xkcd.com/1445/]strips are totally me.

HunchBluntley: DUDE, spoilers! I'm only on #792, and I don't want to skip ahead!

=P

adaliabooks: Wait, you read them in order? :P

adaliabooks: I just hit random until I find one I haven't seen (which doesn't happen much now, I'm sure I've read most of them)

HunchBluntley: I was joking about the "no spoilers" bit, but yeah, I do tend to read all web comics from the beginning, regardless of whether or not there's anything like a narrative or continuity.
Though I only very rarely read web comics these days. Or blogs, for that matter. [hangs head]

HunchBluntley: Speaking of inefficiency... :P