You don't need map(str, INPUT_txt.split(","))
- the elements are already strings. Other than that, its just a matter of cleaning up the split filenames by stripping whitespace.
INPUT_txt = raw_input("Input File(s): ")
element = [ss for ss in (s.strip() for s in INPUT_txt.split(",")) if ss]
for filename in element:
print os.path.abspath(filename)
print os.path.isfile(filename)