The directory Dates16 contains several folders like a show you below in the first list and each folder has a lot of .txt files. I would like to rename those files like I show you in second list
for i in oldNames:
for j in newNames:
Traceback (most recent call last):
File "<stdin>", line 3, in <module>
OSError: [Errno 2] No such file or directory
for i in oldNames: for j in newNames:
This is the problem. You're changing the filename of each oldName J times, even though after the first time the file doesn't exist anymore (because it's been renamed).