Importing astropy and Sub-packages#

In order to encourage consistency among 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’s best to import the desired sub-package with the syntax:

>>> from astropy import subpackage  

For example, to access the FITS-related functionality, you can import with:

>>> from import fits
>>> hdulist ='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.SkyCoord(ra=10.68458*u.deg, dec=41.26917*u.deg, frame='icrs')  
<SkyCoord (ICRS): (ra, dec) in deg
    ( 10.68458,  41.26917)>

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 never importing any Astropy functionality using *, for example:

>>> from 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 import fits as pyfits

Getting Started with Sub-packages#

Because different sub-packages have very different functionalities, each sub-package has its own getting started guide. These can be found by browsing the sections listed in the User Guide.

You can also look at docstrings for a particular package or object, or access their documentation using the find_api_page function. For example,

>>> from astropy import find_api_page
>>> from astropy.units import Quantity
>>> find_api_page(Quantity)  

will bring up the documentation for the Quantity class in your browser.