Where is the source code for PyPI, the Python package index?

The PyPI source can be found here. More technical documents about PyPI's architecture are:

• CheeseShop (general overview with various links)
• CheeseShopDev (technical documentation)

The name CheeseShop is an older name for the Python Package Index (PyPI).

Warehouse is the beautiful, modern replacement for PyPI. It will eventually reach feature parity and replace the older system.