Thanks to the help I got here, I am now very near to achieving my goal namely storing information about the vertices so that I can select them according to their U (from 0 to 1000) and V (from 0 to 1000) indices (and not coordinates).
I want to know if there is, in Blender 3.12 Python, a built in way to select a loop (u or v) when one vertex is selected (equivalent to ALT + click) or how to use the Select_Next() , Select_Previous() and Select_I_Forgot_what(start, number, offset), which would solve my problem in one go. The thing is they seem to work on the vertex’s Index and not with the UV loops. Or, in the worst scenario, I want to use the Select_More() operator at vertex level. Has anyone a working example of a script using this? The more basic the better.