Stainless wasn't offered until 1983 for the Python and by coincidence the T prefix began in 1983. Nickel will have an almost yellow hue when compared to the bright stainless steel. If the gentleman will remove the rubber grips a prominent "N" would be on the grip frame if a nickel finished Python (not to be confused with the "INS" raised lettering for inspected). In all probability the revolver you are looking at is the stainless finish but without more information like DOB or at least the serial number so we can date the firearm it's hard to say for certain. Pictures, especially closeups are always a plus.