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.. currentmodule:: astropy.io.fits
Miscellaneous Features
**********************
This section describes some of the miscellaneous features of :mod:`astropy.io.fits`.
.. _io-fits-differs:
Differs
=======
The :mod:`astropy.io.fits.diff` module contains several facilities for
generating and reporting the differences between two FITS files, or two
components of a FITS file.
The :class:`FITSDiff` class can be used to generate and represent the
differences between either two FITS files on disk, or two existing
:class:`HDUList` objects (or some combination thereof).
Likewise, the :class:`HeaderDiff` class can be used to find the differences
just between two :class:`Header` objects. Other available differs include
:class:`HDUDiff`, :class:`ImageDataDiff`, :class:`TableDataDiff`, and
:class:`RawDataDiff`.
Each of these classes are instantiated with two instances of the objects that
they diff. The returned diff instance has a number of attributes starting with
``.diff_`` that describe differences between the two objects.
Example
-------
..
EXAMPLE START
Generating Differences Between FITS Files Using astropy.io.fits.diff
The :class:`HeaderDiff` class can be used to find the differences
between two :class:`Header` objects like so::
>>> from astropy.io import fits
>>> header1 = fits.Header([('KEY_A', 1), ('KEY_B', 2)])
>>> header2 = fits.Header([('KEY_A', 3), ('KEY_C', 4)])
>>> diff = fits.diff.HeaderDiff(header1, header2)
>>> diff.identical
False
>>> diff.diff_keywords
(['KEY_B'], ['KEY_C'])
>>> diff.diff_keyword_values
defaultdict(..., {'KEY_A': [(1, 3)]})
See the API documentation for details on the different differ classes.
..
EXAMPLE END
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