Astropy Core Package Utilities (astropy.utils)


The astropy.utils package contains general-purpose utility functions and classes. Examples include data structures, tools for downloading and caching from URLs, and version intercompatibility functions.

This functionality is not astronomy-specific, but is intended primarily for use by Astropy developers. It is all safe for users to use, but the functions and classes are typically more complicated or specific to a particuly need of Astropy.

Because of the mostly standalone and grab-bag nature of these utilities, they are generally best understood through their docstrings, and hence this documentation does not have detailed sections like the other packages.


The astropy.utils.compat subpackage is not included in this documentation. It contains utility modules for compatibility with older/newer versions of python, as well as including some bugfixes for the stdlib that are important for Astropy. It is recommended that developers at least glance over the source code for this subpackage, but it cannot be reliably included here because of the large amount of version-specific code it contains.


astropy.utils.misc Module

A “grab bag” of relatively small general-purpose utilities that don’t have a clear module/package to live in.


find_current_module([depth, finddiff]) Determines the module/package from which this function is called.
isiterable(obj) Returns True if the given object is iterable.
deprecated(since[, message, name, ...]) Used to mark a function as deprecated.
deprecated_attribute(name, since[, message, ...]) Used to mark a public attribute as deprecated.
format_exception(msg, *args, **kwargs) Given an exception message string, uses new-style formatting arguments {filename}, {lineno}, {func} and/or {text} to fill in information about the exception that occurred.


lazyproperty Works similarly to property(), but computes the value only once.
NumpyRNGContext(seed) A context manager (for use with the with statement) that will seed the numpy random number generator (RNG) to a specific value, and then restore the RNG state back to whatever it was before.

astropy.utils.collections Module

A module containing specialized collection classes.


HomogeneousList(types[, values]) A subclass of list that contains only elements of a given type or types.

astropy.utils.console Module

Utilities for console input and output.


isatty(file) Returns True if file is a tty.
color_print(*args, **kwargs) Prints colors and styles to the terminal uses ANSI escape sequences.
human_time(seconds) Returns a human-friendly time string that is always exactly 6 characters long.
print_code_line(line[, col, file, tabwidth, ...]) Prints a line of source code, highlighting a particular character position in the line.


ProgressBar(total[, file]) A class to display a progress bar in the terminal.
Spinner(msg[, color, file, step, chars]) A class to display a spinner in the terminal.
ProgressBarOrSpinner(total, msg[, color, file]) A class that displays either a ProgressBar or Spinner depending on whether the total size of the operation is known or not.

File Downloads Module

This module contains helper functions for accessing, downloading, and caching data files.


get_readable_fileobj(*args, **kwds) Given a filename or a readable file-like object, return a context manager that yields a readable file-like object.
get_file_contents(name_or_obj[, encoding, cache]) Retrieves the contents of a filename or file-like object.
get_pkg_data_fileobj(data_name[, encoding, ...]) Retrieves a data file from the standard locations for the package and provides the file as a file-like object that reads bytes.
get_pkg_data_filename(data_name) Retrieves a data file from the standard locations for the package and provides a local filename for the data.
get_pkg_data_contents(data_name[, encoding, ...]) Retrieves a data file from the standard locations and returns its contents as a bytes object.
get_pkg_data_fileobjs(datadir[, pattern, ...]) Returns readable file objects for all of the data files in a given directory that match a given glob pattern.
get_pkg_data_filenames(datadir[, pattern]) Returns the path of all of the data files in a given directory that match a given glob pattern.
compute_hash(localfn) Computes the MD5 hash for a file.
clear_download_cache([hashorurl]) Clears the data file cache by deleting the local file(s).
download_file(remote_url[, cache]) Accepts a URL, downloads and optionally caches the result returning the filename, with a name determined by the file’s MD5 hash.


CacheMissingWarning This warning indicates the standard cache directory is not accessible, with the first argument providing the warning message.


The astropy.utils.xml.* modules provide various XML processing tools.

astropy.utils.xml.check Module

A collection of functions for checking various XML-related strings for standards compliance.

check_anyuri(uri) Returns True if uri is a valid URI as defined in RFC 2396.
check_id(ID) Returns True if ID is a valid XML ID.
check_mime_content_type(content_type) Returns True if content_type is a valid MIME content type (syntactically at least), as defined by RFC 2045.
check_token(token) Returns True if token is a valid XML token, as defined by XML Schema Part 2.
fix_id(ID) Given an arbitrary string, create one that can be used as an xml id.

astropy.utils.xml.iterparser Module

This module includes a fast iterator-based XML parser.

get_xml_iterator(*args, **kwds) Returns an iterator over the elements of an XML file.
get_xml_encoding(source) Determine the encoding of an XML file by reading its header.
xml_readlines(source) Get the lines from a given XML file.

astropy.utils.xml.validate Module

Functions to do XML schema and DTD validation. At the moment, this makes a subprocess call to xmllint. This could use a Python-based library at some point in the future, if something appropriate could be found.

validate_schema(filename, schema_file) Validates an XML file against a schema or DTD.

astropy.utils.xml.writer Module

Contains a class that makes it simple to stream out well-formed and nicely-indented XML.

xml_escape(s) Escapes &, ‘, ”, < and > in an XML attribute value.
xml_escape_cdata(s) Escapes &, < and > in an XML CDATA string.
XMLWriter(file) A class to write well-formed and nicely indented XML.