Getting Started with Astropy

Importing Astropy

In order to encourage consistency amongst users in importing and using Astropy functionality, we have put together the following guidelines.

Since most of the functionality in Astropy resides in sub-packages, importing astropy as:

>>> import astropy

is not very useful. Instead, it is best to import the desired sub-pacakge with the syntax:

>>> from astropy import subpackage

For example, to access the FITS-related functionality, you can import astropy.io.fits with:

>>> from astropy.io import fits
>>> hdulist = fits.open('data.fits')

In specific cases, we have recommended shortcuts in the documentation for specific sub-packages, for example:

>>> from astropy import units as u
>>> from astropy import coordinates as coord
>>> coord.ICRSCoordinates(ra=10.68458, dec=41.26917, unit=(u.degree, u.degree))
<ICRSCoordinates RA=10.68458 deg, Dec=41.26917 deg>

Finally, in some cases, most of the required functionality is contained in a single class (or a few classes). In those cases, the class can be directly imported:

>>> from astropy.cosmology import WMAP7
>>> from astropy.table import Table
>>> from astropy.wcs import WCS

Note that for clarity, and to avoid any issues, we recommend to never import any Astropy functionality using *, for example:

>>> from astropy.io.fits import *  # NOT recommended

Some components of Astropy started off as standalone packages (e.g. PyFITS, PyWCS), so in cases where Astropy needs to be used as a drop-in replacement, the following syntax is also acceptable:

>>> from astropy.io import fits as pyfits