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**************************************
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 # doctest: +SKIP
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') # doctest: +SKIP
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') # doctest: +FLOAT_CMP
<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 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
*********************************
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 :ref:`user-docs`.
You can also look at docstrings for a particular package or object, or access
their documentation using the `~astropy.utils.misc.find_api_page` function. For
example, ::
>>> from astropy import find_api_page
>>> from astropy.units import Quantity
>>> find_api_page(Quantity) # doctest: +SKIP
will bring up the documentation for the `~astropy.units.Quantity` class
in your browser.
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