If you don't need native Python library, considering using an established neural network library with Python bindings. For instance FANN (Fast Artificial Neural network Library) provides such binding.
If you explicitly need a library written in Python, I would suggest checking out Orange. Orange is an open source data visualization and analysis platform that can be either used as a library or a full GUI. it does not readily support everything you might need, but potentially you will find modules suitable work neural networks, such as Orange SNNS module (not sure about its stability though). If you need to write a module of your own, Orange is a good candidate for a platform since it provides you with some basic tools.
