nothing is wrong with it, it is just not backward compatible with python 2, you'd have to script completely in python 3 to use it, and you wouldn't be able to mix in old scripts if you wanted
as for your error, you've got something laid out incorrectly, not sure if gedit is capable of highlighting syntax errors in python, if it is, they would be highlighted yellow where it can potentially be a problem for the parser.
# A comment, this is so you can read your program later.
# Anything after the # is ignored by python.
print "I could have code like this." # and the comment after is ignored
# You can also use a comment to "disable" or comment out a piece of code:
# print "This won't run."
print "This will run."