astropy has the following strict requirements:

astropy also depends on other packages for optional features:

  • scipy 0.18 or later: To power a variety of features in several modules.

  • h5py: To read/write Table objects from/to HDF5 files.

  • BeautifulSoup: To read Table objects from HTML files.

  • html5lib: To read Table objects from HTML files using the pandas reader.

  • bleach: Used to sanitize text when disabling HTML escaping in the Table HTML writer.

  • PyYAML: To read/write Table objects from/to the Enhanced CSV ASCII table format and to serialize mixins for various formats.

  • xmllint: To validate VOTABLE XML files. This is a command line tool installed outside of Python.

  • pandas: To convert Table objects from/to pandas DataFrame objects. Version 0.14 or higher is required to use the Pandas I/O functions to read/write Table objects.

  • bintrees for faster FastRBT and FastBST indexing engines with Table, although these will still be slower in most cases than the default indexing engine.

  • sortedcontainers for faster SCEngine indexing engine with Table, although this may still be slower in some cases than the default indexing engine.

  • pytz: To specify and convert between timezones.

  • jplephem: To retrieve JPL ephemeris of Solar System objects.

  • matplotlib 2.0 or later: To provide plotting functionality that astropy.visualization enhances.

  • scikit-image: To downsample a data array in astropy.nddata.utils.

  • setuptools: Used for discovery of entry points which are used to insert fitters into astropy.modeling.fitting.

  • mpmath: Used for the ‘kraft-burrows-nousek’ interval in poisson_conf_interval.

  • asdf 2.3 or later: Enables the serialization of various Astropy classes into a portable, hierarchical, human-readable representation.

  • bottleneck: Improves the performance of sigma-clipping and other functionality that may require computing statistics on arrays with NaN values.

And the following packages can optionally be used when testing:

However, note that these packages require installation only if those particular features are needed. astropy will import even if these dependencies are not installed.

Installing astropy

Using pip


Users of the Anaconda Python distribution should follow the instructions for Using Conda.

To install astropy with pip, run:

pip install astropy

If you want to make sure none of your existing dependencies get upgraded, you can also do:

pip install astropy --no-deps

On the other hand, if you want to install astropy along with all of the available optional dependencies, you can do:

pip install astropy[all]

Note that you will need a C compiler (e.g. gcc or clang) to be installed (see Building from source below) for the installation to succeed.

If you get a PermissionError this means that you do not have the required administrative access to install new packages to your Python installation. In this case you may consider using the --user option to install the package into your home directory. You can read more about how to do this in the pip documentation.

Alternatively, if you intend to do development on other software that uses astropy, such as an affiliated package, consider installing astropy into a virtualenv.

Do not install astropy or other third-party packages using sudo unless you are fully aware of the risks.

Using Conda

astropy is installed by default with the Anaconda Distribution. To update to the latest version run:

conda update astropy

There may be a delay of a day or two between when a new version of astropy is released and when a package is available for Anaconda. You can check for the list of available versions with conda search astropy.


Attempting to use pip to upgrade your installation of astropy may result in a corrupted installation.

Testing an Installed astropy

The easiest way to test if your installed version of astropy is running correctly is to use the astropy.test() function:

import astropy

The tests should run and print out any failures, which you can report at the Astropy issue tracker.

This way of running the tests may not work if you do it in the astropy source distribution. See Testing a Source Code Build of astropy for how to run the tests from the source code directory, or Running Tests for more details.

Building from Source


You will need a compiler suite and the development headers for Python and NumPy in order to build astropy.

If you are building the latest developer version rather than using a stable release, you will also need Cython (v0.29.13 or later) and jinja2 (v2.7 or later) installed. The released packages have the necessary C files packaged with them, and hence do not require Cython.

Prerequisites for Linux

On Linux, using the package manager for your distribution will usually be the easiest route to making sure you have the prerequisites to build astropy. In order to build from source, you will need the Python and Numpy development package for your Linux distribution, as well as a number of helper packages.

For Debian/Ubuntu:

sudo apt-get install python3-dev python3-numpy-dev python3-setuptools cython3 python3-jinja2 python3-pytest-astropy

For Fedora/RHEL:

sudo yum install python3-devel python3-numpy python3-setuptools python3-Cython python3-jinja2 python3-pytest-astropy


Building the developer version of astropy may require newer versions of the above packages than are available in your distribution’s repository. If so, you could either try a more up to date version (such as Debian testing), or install more up-to-date versions using pip or conda in a virtual environment.

Prerequisites for Mac OS X

On MacOS X you will need the XCode command line tools which can be installed using:

xcode-select --install

Follow the onscreen instructions to install the command line tools required. Note that you do not need to install the full XCode distribution (assuming you are using MacOS X 10.9 or later).

The instructions for building NumPy from source are a good resource for setting up your environment to build Python packages.

Obtaining the Source Packages

Source Packages

The latest stable source package for astropy can be downloaded here.

Development Repository

The latest development version of astropy can be cloned from GitHub using this command:

git clone --recursive git://

If you wish to participate in the development of astropy, see Developer Documentation. This document covers only the basics necessary to installing astropy.

Building and Installing

astropy uses the Python built-in distutils framework for building and installing, and requires the setuptools package.

If NumPy is not already installed in your Python environment, the astropy setup process will try to download and install it before continuing to install astropy.

To build and install astropy (from the root of the source tree):

pip install .

If you install in this way and you make changes to the code, you will need to re-run the install command for changes to be reflected. Alternatively, you can use:

pip install -e .

which installs astropy in develop/editable mode, which means that changes in the code are immediately reflected in the installed version.


If you get an error mentioning that you do not have the correct permissions to install astropy into the default site-packages directory, you can try installing with:

pip install . --user

which will install into a default directory in your home directory.

External C Libraries

The astropy source ships with the C source code of a number of libraries. By default, these internal copies are used to build astropy. However, if you wish to use the system-wide installation of one of those libraries, you can pass one or more of the --use-system-X flags to the build command.

For example, to build astropy using the system libexpat, use:

python build --use-system-expat

To build using all of the system libraries, use:

python build --use-system-libraries

To see which system libraries astropy knows how to build against, use:

python build --help

As with all distutils command line options, they may also be provided in a setup.cfg in the same directory as For example, to use the system libexpat, add the following to the setup.cfg file:


The C libraries currently bundled with astropy include:

  • wcslib see cextern/wcslib/README for the bundled version.

  • cfitsio see cextern/cfitsio/changes.txt for the bundled version.

  • erfa see cextern/erfa/README.rst for the bundled version.

  • expat see cextern/expat/README for the bundled version.

Installing astropy into CASA

If you want to be able to use astropy inside CASA, the easiest way is to do so from inside CASA.

First, we need to make sure pip is installed. Start up CASA as normal, and then type:

CASA <2>: from setuptools.command import easy_install

CASA <3>: easy_install.main(['--user', 'pip'])

Now, quit CASA and re-open it, then type the following to install astropy:

CASA <2>: import subprocess, sys

CASA <3>: subprocess.check_call([sys.executable, '-m', 'pip', 'install', '--user', 'astropy'])

Then close CASA again and open it, and you should be able to import astropy:

CASA <2>: import astropy

Any astropy affiliated package can be installed the same way (e.g. the spectral-cube or other packages that may be useful for radio astronomy).


The above instructions have not been tested on all systems. We know of a few examples that do work, but that is not a guarantee that this will work on all systems. If you install astropy and begin to encounter issues with CASA, please look at the known CASA issues and if you do not encounter your issue there, please post a new one.

Building Documentation


Building the documentation is in general not necessary unless you are writing new documentation or do not have internet access, because the latest (and archive) versions of Astropy’s documentation should be available at .


Building the documentation requires the astropy source code and some additional packages, including those in Requirements. The easiest way to install the extra dependencies for documentation is to install the sphinx-astropy package, either with pip:

pip install sphinx-astropy

or with Conda:

conda install -c astropy sphinx-astropy

In addition to providing configuration common to packages in the Astropy ecosystem, this package also serves as a way to automatically get the main dependencies, including:

  • Sphinx - the main package we use to build the documentation

  • astropy-sphinx-theme - the default ‘bootstrap’ theme used by astropy and a number of affiliated packages

  • sphinx-automodapi - an extension that makes it easy to automatically generate API documentation

  • sphinx-gallery - an extension to generate example galleries

  • numpydoc - an extension to parse docstrings in NumPyDoc format

  • pillow - used in one of the examples

In addition, if you want inheritance graphs to be generated, you will need to make sure that Graphviz is installed. If you install sphinx-astropy with Conda, Graphviz will automatically get installed, but if you use pip, you will need to install Graphviz separately as it is not a Python package.


There are two ways to build the Astropy documentation. The first way is to execute the command (from the astropy source directory):

python build_docs

The documentation will be built in the docs/_build/html directory, and can be read by pointing a web browser to docs/_build/html/index.html.

In the second way, LaTeX documentation can be generated by using the command:

python build_docs -b latex

The LaTeX file Astropy.tex will be created in the docs/_build/latex directory, and can be compiled using pdflatex.

The above method builds the API documentation from the source code. Alternatively, you can do:

cd docs
make html

And the documentation will be generated in the same location, but using the installed version of astropy.

Reporting Issues/Requesting Features

As mentioned above, building the documentation depends on a number of sphinx extensions and other packages. Since it is not always possible to know which package is causing issues or would need to have a new feature implemented, you can open an issue in the core astropy package issue tracker. However, if you wish, you can also open issues in the repositories for some of the dependencies:

  • For requests/issues related to the appearance of the docs (e.g. related to the CSS), you can open an issue in the astropy-sphinx-theme issue tracker.

  • For requests/issues related to the auto-generated API docs which appear to be general issues rather than an issue with a specific docstring, you can use the sphinx-automodapi issue tracker.

  • For issues related to the default configuration (e.g which extensions are enabled by default), you can use the sphinx-astropy issue tracker.

Testing a Source Code Build of astropy

Before running tests, it is necessary to make sure that Astropy’s test dependencies are installed. This can be done with the following command:

pip install pytest-astropy

More information on what the pytest-astropy package provides can be found in Testing Dependencies.

The most convenient way to test that your Astropy built correctly (without installing astropy) is to run this from the root of the source tree:

python test

There are also alternative methods of Running Tests. Note that you will need pytest to be installed for this to work.