A Pereskiopsis cacti (I think) They're tropical dryer side. All day max sun? No doubt it'll fry and fry fast even with good transitioning. They like warm air with some direct with modest UV rays. IME about the same sun and heat as a holiday cati but could sometimes use less watering by volume it can also be kept on a dryer side than a holiday in frequencies of watering best of luck to you or them.

Direct for an hour with max summer UV sun rays IIRC the trunk will start to fold and wrinkle when to long in warm direct,early thru mid fall when cooler they can handle more direct sun times but would keep the late season direct sun exposure to 2.5 - 3 hours max. For summer all it needs is a fare share of some direct with some heavy to modest shaded sun.

If they didn't get so darn tall I'd still have one sitting on a morning sun window sill for the summer kicking it outside during the early fall only to drag it back in prior to any frost.

I don't grown cacti, just mostly succulents, but I suggest unless he exposes the plant to the sun GRADUALLY. like a few hours every day, it will burn. (I grew up in Rio & know what hot summer is near there.)

Its definitely an Opuntia subulata. They do like full sun, but as said above, transition slowly into full sun. I have several thriving in full sun.

Are those stones around the base of it? If so, and in intense sun they will warm up so much they could burn the bases of the stems...I would remove them, just my thoughts!

Gill

Austrocylindropuntia subulata (also called Opuntia subulata). They are native to dry Andean valleys in Peru, and like very intense sun. In heat zone 7 I think it should be fine in full sun, as long as it is transitioned gently. It may drop its leaves, grow spinier, and look a little more like a North American Cholla (Cylindropuntia), but I don't think it will fry. Here in Tucson, Arizona they look best grown in filtered sun, such as under a tree, but we are in heat zone 10, with a scorching desert climate.

Not cold hardy enough for zone 7 normally... mine burn here in zone 8b every winter as soon as it gets down to 20F. At least identification correct (A subulata).

Sao Paolo is in heat zone 7, with 61-90 days above 86F each year. Record highs for summer months are in the mid 90's. It is in hardiness zone 11b.

THANK YOU EVERYONE (nomen_nudum,
Karen
R. Sternberg, garrett222,
Gill, kenizona,
palmbob) for your input, its greatly appreciated. I will show your comments to my friend (plant owner). THANK YOU one more time !!!! :)