how can I make a suggestion for a new feature in python
Perhaps post your idea on the Python mailing list
It really depends on the nature of the suggestion.
If it's a bug, it should definitely be put on the tracker. Otherwise, it probably should not go in the tracker right away. Python developers have specifically asked that the tracker not be used to create discussions, but to track implementation-specific aspects.
You can also post to Python-dev, though you should also be careful there also. Python is a complex project. Because it's more of a platform than a project, it has vastly more restrictions on it than a typical open-source application. Therefore, developers will be resistant to any change which isn't an immediate and obvious benefit. In general, I would advise against posting to Python-dev unless you've had at least some time to read through some of the interactions there to get a feel for the types of suggestions and discussions that go on there.
Generally, I think the python-dev list would recommend you post first to comp.lang.python and start a discussion. Rally some support from a vetted Python maintainer and others in the community. Be sure to show that you have considered the negative implications of any change you are considering and how you would mitigate them. A lot of times, it's good at this stage to have a reference implementation (maybe even something on the package index) that others can install--if it is indeed useful, people will use it and the need will be more apparent. After you've gathered some support from the community, you can then move it (possibly) to python-dev to get more feedback from the core developers before submitting a PEP (Python Enhancement Proposal).
Good luck!
Python is Open Source, which means that all of these processes are very open. It also means that you will have far more success if you implement the suggestion and prove its merits yourself.
Normally you should establish that your proposal is a good way to solve the particular problem. This can be discussed in comp.lang.python or python-list.
A more serious suggestion's details can be ironed out on the mailing list python-ideas. This is normally a free forum for proposals.
When the proposal is finally ready, and you think it might be approved, it can be submitted as a Python Enhancement Proposal (PEP) to the mailing list python-dev. Posting on python-dev prematurely will probably not lead to good results. For many years now, most significant changes in Python have gone through the PEP process.
This answer is written in all generality; writing a PEP for a single added decorator is probably overkill, it's something that is more expected for, exactly, a new keyword or so.
You can add your suggestion to the issue tracker http://bugs.python.org/. they usually implement things posted there.