Pfft. 3D print the fancy bit, the rest is a half dozen screws and a lick of paint.

Ok, I'll just fire up my 3D printer. Oh, hang on...

I'm hanging...

Ah right. It turns out I haven't got a 3D printer. 

However, since the collective web madskillz of teh forum (including mine) have yet to locate the springy hook I longed for, I've decide to screw a wooden block with a rubber doorstop to the decking over which the door opens. I'll also cast a concrete lump with rope attached in an old plastic flower pot. The combination should hold the door still in windy weather.

I have.

Wonder if I could print something suitable. My guess is with PLA it would maybe melt in the sun. Or maybe not if it was white rather than black.

Is PLA stiff (like acrylic plastics) when printed, or flexible like nylon, PVA etc? How is it under stress - its tensegrity as it were? As in subject to continuous tension from a steel spring. I'm thinking that 3D printing may not be what I'm after. 

I'm thinking the first strong gust of wind would blow it into the weeds.

Depends how thick you print it, of course. This vessel I printed has a wall varying from 2-4mm and has no visible flex to the tightest grip I dare do short of breaking it. Of course it's an inherently strong shape, ribbed, not for pleasure, but for internal strength. 

The wall isn't solid, of course: the printing software automatically fills any thickness with honeycomb that's more air than plastic.

So, you're saying I could fill that with concrete and it would hold my patio door open?

There are these cheap pole lamps from China you can buy at walmart. We've had a couple. They consist of several sections of pole you screw together, the light fixture, and a weighted base that looks and feels solid, but is an incredibly thin plastic shell filled with plaster of paris. After 3-4 years the plastic deteriorates, with predictable consequences.

Yours for a song. And it will fill your soul daily with delight.

Then do the whole thing from wood - it only needs to be more attractive than a concrete filled flower pot on a rope.

Are you saying a concrete filled flower pot on a rope is unattractive?

https://www.wish.com/product/5d4e3cf17319d63a0e86c8f2

This is TOO easy!  :-(

It would take a lot of make up to make me want to make out with one. Do you not agree?

The whole point is to swing it around your head.

Yes, I'd seen this one on my travels around the web. Right idea but probably not substantial enough for a patio door - or wide enough, as the door is 8 cm. And I suspect the easily removable sticky fixing pad might not last beyond the first downpour.

I did love the write-up though. "Simple but magical". Also, and this nearly sold it to me, "No accident: there are always accidents when you squat to keep the traditional one in place..."

Personally, I'm always having accidents when I squat, and I never squat so often as when I'm trying to hold a door open. Or maybe 'squatting to keep the traditional one in place' is a euphemism.

...It's what the laydeeeez always say to me.

Around your head and nowhere near them?