In Python 3:

Either split a file or join two files.

If you choose to split a file, ask the user for the file name, read the file line by line into a list. Write half the list to a new file and the other half to another new file.

If you choose to join two files, ask the user for the names of the two files they want to join. Read the two files and write the first file, then the second file to a new file.

Handle all Exceptions using a try/except. Document your program fully.