Abus Bordo Lite mini 6055
It’s a folding key-lock lock that works like grampa’s articulated ruler, but the arms are made of steel alloys, so it’s not just light, but compact, too. It won’t fit around a fat tree, but a metal pole, no problem.
And it seems to be the best compromise of security and light weight for multi-hour, out-of-sight lockage during the day in low-to-medium risk portions of cities.
Weight: just under a pound
Made in: Germany. Comes with 2 keys.
Shown alongside a waterbottle (not included) for scale purposes.
Folded size: 6" x 1.9" x 1.125" (15.2cm x 4.9cm x 2.8cm)
Unfolded length: 23.5" (60cm) long