Here we describe a broad overview of the Astropy project and its parts.
The “Astropy Project” is distinct from the astropy package. The Astropy Project is a process intended to facilitate communication and interoperability of python packages/codes in astronomy and astrophysics. The project thus encompasses the astropy core package (which provides a common framework), all “affiliated packages” (described below in Affiliated Packages), and a general community aimed at bringing resources together and not duplicating efforts.
The astropy package (alternatively known as the “core” package) contains various classes, utilities, and a packaging framework intended to provide commonly-used astronomy tools. It is divided into a variety of sub-packages, which are documented in the remainder of this documentation (see User Documentation for documentation of these components).
The core also provides this documentation, and a variety of utilities that simplify starting other python astronomy/astrophysics packages. As described in the following section, these simplify the process of creating affiliated packages.
The Astropy project includes the concept of “affiliated packages.” An affiliated package is an astronomy-related python package that is not part of the astropy core source code, but has requested to be included in the Astropy project. Such a package may be a candidate for eventual inclusion in the main astropy package (although this is not required).
There is a registry of affiliated packages at http://affiliated.astropy.org, and in the near future, the astropy core will include a tool to install affiliated packages by name. See the config module documentation for details about the affiliated package registry and install tool. Note that affiliated packages do not use the astropy namespace, which is reserved for the core. Instead, they either use their package name directly, or awastropy.packagename (“affiliated with astropy”).
If you are interested in starting an affiliated package, or have a package you are interested in making more compatible with astropy, the astropy core package includes a variety of features that simplify and homogenize package management. Astropy provides a package template that provides a common way to organize packages, to make your life simpler. You can use this template either with a new package you are starting or an existing package to make it more compatible with Astropy and the affiliated package installer. See the usage instructions in the template for further details.
Aside from the actual code, Astropy is also a community of astronomy-associated users and developers that agree that sharing utilities is healthy for the community and the science it produces. This community is of course central to accomplishing anything with the code itself.