Merging two files into one .CSV
You should never do this:

for OS in OS:


Your loop variable "OS" is the same name as the iterator you're looping over.  That is very likely to cause you problems.  In some simple cases it will work, but makes for very unreadable code.

Secondly, for every line in the first file you are reading the ENTIRE second file!  So you read the second file as many times as there are lines in the first.  You need to separate the loops, read the first file (I like using input_fileVms.readlines() to put everything in a list of strings) and then read the second file.  Once you have the contents of the two files in data structures, then you can merge them.  Unless your files are in the 1GB range, this is what I would recommend.  If you are just concatenating the files, you don't need csv.reader() because there is no reason to split out the strings and get the individual fields.