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Describe how to populate mode and size

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Andrew Murray 2023-10-15 16:17:19 +11:00
parent 4ace56d214
commit a1ddb4dd27
1 changed files with 15 additions and 15 deletions
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docs/handbook/writing-your-own-image-plugin.rst
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@ -26,14 +26,14 @@ Pillow decodes files in two stages:
it. it.
An image plugin should contain a format handler derived from the An image plugin should contain a format handler derived from the
:py:class:`PIL.ImageFile.ImageFile` base class. This class should :py:class:`PIL.ImageFile.ImageFile` base class. This class should provide an
provide an ``_open`` method, which reads the file header and ``_open`` method, which reads the file header and set at least the internal
sets up at least the :py:attr:`~PIL.Image.Image.mode` and ``_size`` and ``_mode`` attributes so that :py:attr:`~PIL.Image.Image.mode` and
:py:attr:`~PIL.Image.Image.size` attributes. To be able to load the :py:attr:`~PIL.Image.Image.size` are populated. To be able to load the file,
file, the method must also create a list of ``tile`` descriptors, the method must also create a list of ``tile`` descriptors, which contain a
which contain a decoder name, extents of the tile, and decoder name, extents of the tile, and any decoder-specific data. The format
any decoder-specific data. The format handler class must be explicitly handler class must be explicitly registered, via a call to the
registered, via a call to the :py:mod:`~PIL.Image` module. :py:mod:`~PIL.Image` module.
.. note:: For performance reasons, it is important that the .. note:: For performance reasons, it is important that the
``_open`` method quickly rejects files that do not have the ``_open`` method quickly rejects files that do not have the
@ -96,13 +96,13 @@ true color.
) )
The format handler must always set the The format handler must always set the internal ``_size`` and ``_mode``
:py:attr:`~PIL.Image.Image.size` and :py:attr:`~PIL.Image.Image.mode` attributes so that :py:attr:`~PIL.Image.Image.size` and
attributes. If these are not set, the file cannot be opened. To :py:attr:`~PIL.Image.Image.mode` are populated. If these are not set, the file
simplify the plugin, the calling code considers exceptions like cannot be opened. To simplify the plugin, the calling code considers exceptions
:py:exc:`SyntaxError`, :py:exc:`KeyError`, :py:exc:`IndexError`, like :py:exc:`SyntaxError`, :py:exc:`KeyError`, :py:exc:`IndexError`,
:py:exc:`EOFError` and :py:exc:`struct.error` as a failure to identify :py:exc:`EOFError` and :py:exc:`struct.error` as a failure to identify the
the file. file.
Note that the image plugin must be explicitly registered using Note that the image plugin must be explicitly registered using
:py:func:`PIL.Image.register_open`. Although not required, it is also a good :py:func:`PIL.Image.register_open`. Although not required, it is also a good