The first backslash in your string is being interpreted as a special character, in fact because it's followed by a "U" it's being interpreted as the start of a unicode code point.
To fix this you need to escape the backslashes in the string. I don't know Python specifically but I'd guess you do it by doubling the backslashes:
data = open("C:\\Users\\miche\\Documents\\school\\jaar2\\MIK\\2.6\\vektis_agb_zorgverlener")