tmp = files
for file in files:
if not file['parents']:
Update 12/06/2013: Just verify this method, it's wrong (files of a shared folder has parents too). So, user 'owners' attribute instead to check the owners is the authenticated user:
tmp = 
allfiles = search_files(service, "trashed = false")
for file in allfiles:
This is how I solve the issue. Maybe there are many better ways out there, but for now, I just use it.