Configuration system (
The astropy configuration system is designed to give users control of various parameters used in astropy or affiliated packages without delving into the source code to make those changes.
The configuration system got a major overhaul in astropy 0.4 as part of APE3. See Configuration transition for information about updating code to use the new API.
The Astropy configuration options are most easily set by modifying the configuration file. It will be automatically generated with all the default values commented out the first time you import Astropy. You can find the exact location by doing:
>>> from astropy.config import get_config_dir >>> get_config_dir()
And you should see the location of your configuration directory. The standard
scheme generally puts your configuration directory in
but if you’ve set the environment variable
XDG_CONFIG_HOME and the
$XDG_CONFIG_HOME/astropy directory exists, it will instead be there.
This is a slight variation from the behavior of most Linux
applications with respect to
$XDG_CONFIG_HOME, where the
$XDG_CONFIG_HOME is not defined, would be to put
Once you’ve found the configuration file, open it with your favorite editor. It should have all of the sections you might want, with descriptions and the type of the value that is accepted. Feel free to edit this as you wish, and any of these changes will be reflected when you next start Astropy. Or, if you want to see your changes immediately in your current Astropy session, just do:
>>> from astropy.config import reload_config >>> reload_config()
If for whatever reason your
$HOME/.astropy directory is not accessible
(i.e., you have astropy running somehow as root but you are not the root
user), the best solution is to set the
XDG_CACHE_HOME environment variables pointing to directories, and create
astropy directory inside each of those. Both the configuration and
data download systems will then use those directories and never try to
By convention, configuration parameters live inside of objects called
conf at the root of each subpackage. For example, configuration
parameters related to data files live in
This object has properties for getting and setting individual
configuration parameters. For instance to get the default URL for
astropy remote data do:
>>> from astropy.utils.data import conf >>> conf.dataurl 'http://data.astropy.org/'
Changing Values at Run-time¶
Changing configuration values persistently is done by editing the
configuration file as described above. Values can also, however, be
modified in an active python session by setting any of the properties
For example, if there is a part of your configuration file that looks like:
[utils.data] # URL for astropy remote data site. dataurl = http://data.astropy.org/ # Time to wait for remote data query (in seconds). remote_timeout = 3.0
You should be able to modify the values at run-time this way:
>>> from astropy.utils.data import conf >>> conf.dataurl 'http://data.astropy.org/' >>> conf.dataurl = 'http://astropydata.mywebsite.com' >>> conf.dataurl 'http://astropydata.mywebsite.com' >>> conf.remote_timeout 3.0 >>> conf.remote_timeout = 4.5 >>> conf.remote_timeout 4.5
Instead of modifying the variables in python, you can also modify the configuration files and then reload them. For example, if you modify the configuration file to say:
[utils.data] # URL for astropy remote data site. dataurl = http://myotherdata.mywebsite.com/ # Time to wait for remote data query (in seconds). remote_timeout = 6.3
And then run the following commands:
>>> conf.reload('dataurl') >>> conf.reload('remote_timeout')
This should update the variables with the values from the configuration file:
>>> conf.dataurl 'http://myotherdata.mywebsite.com/' >>> conf.remote_timeout 6.3
You can reload all configuration parameters of a
conf object at
once by calling
reload with no parameters:
Or if you want to reload all astropy configuration at once, use the
You can also reset a configuration parameter back to its default value. Note that this is the default value defined in the Python code, and has nothing to do with the configuration file on disk:
>>> conf.reset('dataurl') >>> conf.dataurl 'http://data.astropy.org/'
Each time you upgrade to a new major version of astropy, the configuration parameters may have changed.
If you never edited your configuration file, there is nothing for you to do. It will automatically be replaced with a configuration file template for the newly installed version of astropy.
If you did customize your configuration file, it will not be touched.
Instead, a new configuration file template will be installed alongside
it with the version number in the filename, for example
astropy.0.4.cfg. You can compare this file to your
astropy.cfg file to see what needs to be changed or updated.
Adding new configuration items¶
Configuration items should be used wherever an option or setting is
needed that is either tied to a system configuration or should persist
across sessions of astropy or an affiliated package. Options that may
affect the results of science calculations should not be configuration
items, but should instead be
it’s possible to reproduce science results without them being affected
by configuration parameters set in a particular environment.
Admittedly, this is only a guideline, as the precise cases where a
configuration item is preferred over, say, a keyword option for a
function is somewhat personal preference. It is the preferred form of
persistent configuration, however, and astropy packages must all use
it (and it is recommended for affiliated packages).
The reference guide below describes the interface for creating a
conf object with a number of configuration parameters. They
should be defined at the top level, i.e. in the
each subpackage that has configuration items:
""" This is the docstring at the beginning of a module """ from astropy import config as _config class Conf(_config.ConfigNamespace): """ Configuration parameters for my subpackage. """ some_setting = _config.ConfigItem( 1, 'Description of some_setting') another_setting = _config.ConfigItem( 'string value', 'Description of another_setting') # Create an instance for the user conf = Conf() ... implementation ... def some_func(): #to get the value of these options, I might do: something = conf.some_setting + 2 return conf.another_setting + ' Also, I added text.'
The configuration items also need to be added to the config file
template. For astropy, this file is in
an affiliated package called, for example,
packagename, the file
packagename/packagename.cfg. For the example above, the
following content would be added to the config file template:
[subpackage] ## Description of some_setting # some_setting = 1 ## Description of another_setting # another_setting = foo
Note that the key/value pairs are commented out. This will allow for
changing the default values in a future version of astropy without
requiring the user to edit their configuration file to take advantage
of the new defaults. By convention, the descriptions of each
parameter are in comment lines starting with two hash characters
##) to distinguish them from commented out key/value pairs.
Item Types and Validation¶
If not otherwise specified, a
ConfigItem gets its
type from the type of the
defaultvalue it is given when it is
created. The item can only be set to be an object of this type.
some_setting = ConfigItem(1, 'A description.') ... conf.some_setting = 1.2
will fail, because
1.2 is a float and
1 is an int.
Note that if you want the configuration item to be limited to a
particular set of options, you should pass in a list as the
defaultvalue option. The first entry in the list will be taken as
the default, and the list as a whole gives all the valid options. For
an_option = ConfigItem( ['a', 'b', 'c'], "This option can be 'a', 'b', or 'c'") ... conf.an_option = 'b' # succeeds conf.an_option = 'c' # succeeds conf.an_option = 'd' # fails! conf.an_option = 6 # fails!
ConfigItem can be explicitly given a type
an_int_setting = ConfigItem( 1, 'A description.', cfgtype='integer') ... conf.an_int_setting = 3 # works fine conf.an_int_setting = 4.2 # fails!
If the default value’s type doesn’t match
ConfigItem cannot be created:
an_int_setting = ConfigItem( 4.2, 'A description.', cfgtype='integer')
In summary, the default behavior (of automatically determining
is usually what you want. The main exception is when you want your
configuration item to be a list. The default behavior will treat that
as a list of options unless you explicitly tell it that the
ConfigItem itself is supposed to be a list:
a_list_setting = ConfigItem([1, 2, 3], 'A description.') a_list_setting = ConfigItem([1, 2, 3], 'A description.', cfgtype='list')
Details of all the valid
cfgtype items can be found in the
validation section of the configobj manual.
Below is a list of the valid values here for quick reference:
Keep in mind is that
ConfigItem objects can be
changed at runtime by users. So it is always recommended to read their
values immediately before use instead of just storing their initial
value to some other variable (or used as a default for a
function). For example, the following will work, but is incorrect
def some_func(val=conf.some_setting): return val + 2
This works fine as long as the user doesn’t change its value during runtime, but if they do, the function won’t know about the change:
>>> some_func() 3 >>> conf.some_setting = 3 >>> some_func() # naively should return 5, because 3 + 2 = 5 3
There are two ways around this. The typical/intended way is:
def some_func(): """ The `SOME_SETTING` configuration item influences this output """ return conf.some_setting + 2
Or, if the option needs to be available as a function parameter:
def some_func(val=None): """ If not specified, `val` is set by the `SOME_SETTING` configuration item. """ return (conf.some_setting if val is None else val) + 2
This module contains configuration and setup utilities for the Astropy project. This includes all functionality related to the affiliated package index.
||Determines the Astropy cache directory name and creates the directory if it doesn’t exist.|
||Gets the configuration object or section associated with a particular package or module.|
||Determines the Astropy configuration directory name and creates the directory if it doesn’t exist.|
||Reloads configuration settings from a configuration file for the root package of the requested package/module.|
||Removed in astropy 0.4.|
||A class that exists to support backward compatibility only.|
||A setting and associated value stored in a configuration file.|
||A namespace of configuration items.|
||A backward-compatibility layer to support the old
||A Warning that is issued when the configuration directory cannot be accessed (usually due to a permissions problem).|
||A Warning that is issued when the configuration value specified in the astropy configuration file does not match the type expected for that configuration value.|
Class Inheritance Diagram¶