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Overview of Astropy File I/O
****************************
Astropy provides two main interfaces for reading and writing data:
- :ref:`High-level Unified I/O <io-unified>` interface that is designed to be consistent
and easy to use. This allows working with different types of data such as
:ref:`tables <astropy-table>`, :ref:`images <astropy_nddata>`, and even
:ref:`cosmologies <cosmology_io>`.
- Low-level I/O sub-packages that are directly responsible for
reading and writing data in specific formats such as :ref:`FITS <astropy-io-fits>`
or :ref:`VOTable <astropy-io-votable>`.
In general we recommend starting with the high-level interface unless you have a
specific need for the low-level interface.
.. list-table:: Comparison of high-level and low-level interfaces
:widths: 50 50
:header-rows: 1
* - High-level Unified I/O
- Low-level I/O
* - Use ``read()`` and ``write()`` class methods of
output data class, e.g., ``data = QTable.read("data.fits")`` returns a
`~astropy.table.QTable`.
- Interfaces are specific to format, e.g., ``hdus = fits.open("data.fits")``
returns an `~astropy.io.fits.HDUList`.
* - Read and write entire file at once.
- Support varies, e.g., :ref:`FITS <astropy-io-fits>` has memory-mapped
read access.
* - Automatically determine file format in common cases.
- Specify format explicitly.
* - Help documentation via class method, e.g., ``QTable.read.help("fits")``.
- Help documentation varies, e.g., ``help(fits.open)`` or API docs.
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