According to YouTube videos, when plumbers need to solder a fitting on to a copper pipe that has water dripping through it, they can plug up the pipe temporarily with a wad of bread. What are alternative methods? Do they make something like a plunger that can be pushed into the pipe to stop the drips? - a plunger whose handle can withstand the heat of soldering.

(I need to solder a fitting on a 3/4 inch copper waterline and I don't know if the shut-off valve at the street is 100% effective.)