import persyst module cross platform paths

Dear MNE team:

In the persyst.py module there is an issue where the script is not platform agnostic in the way that it handles paths. Persyst lay files are only able to generate in windows platforms. So when those files are saved the lay files file section contains a windows path with the location where the file was created. If you try to process these files for analysis in a different computer MacOS or Linux. when you use persyt.py line 112

if key == 'file':
    dat_fname = op.basename(val)

if this is processed in a UNIX based machine it will output the windows path and it wont be able to get the correct basename of the file to extract the DAT file.

The only two ways I can envision this can be corrected is that you can continue to use the os module. But you then have to check if the system being use to process is a UNIX or windows base system by importing the platform python module and checking the type of system. If it is a linux system then you need to do:

import ntpath

dat_fname = ntpath.basename (val)

This indeed will correct the issue; but I am not sure the behavior in a windows machine as I am using linux.

Alternatively, you can dish the OS module all together and use pathlib, this library will handle the paths correctly in a system agnostic manner; but it will mean that you need to change everything where os module is used and make sure users install that library as part of the installation. Not sure what you think.

Andres

Start in persyst.py at line 112 and inspect how the file value from a Persyst .lay file is converted to a DAT basename. Reproduce processing a Windows-style path on a Unix-based system, then verify that the correct DAT file is selected without breaking Windows behavior.