mirror of
https://github.com/python-pillow/Pillow.git
synced 2024-11-10 19:56:47 +03:00
111 lines
3.7 KiB
ReStructuredText
111 lines
3.7 KiB
ReStructuredText
.. _file-handling:
|
|
|
|
File Handling in Pillow
|
|
=======================
|
|
|
|
When opening a file as an image, Pillow requires a filename, ``os.PathLike``
|
|
object, or a file-like object. Pillow uses the filename or ``Path`` to open a
|
|
file, so for the rest of this article, they will all be treated as a file-like
|
|
object.
|
|
|
|
The following are all equivalent::
|
|
|
|
from PIL import Image
|
|
import io
|
|
import pathlib
|
|
|
|
with Image.open("test.jpg") as im:
|
|
...
|
|
|
|
with Image.open(pathlib.Path("test.jpg")) as im2:
|
|
...
|
|
|
|
with open("test.jpg", "rb") as f:
|
|
im3 = Image.open(f)
|
|
...
|
|
|
|
with open("test.jpg", "rb") as f:
|
|
im4 = Image.open(io.BytesIO(f.read()))
|
|
...
|
|
|
|
If a filename or a path-like object is passed to Pillow, then the resulting
|
|
file object opened by Pillow may also be closed by Pillow after the
|
|
``Image.Image.load()`` method is called, provided the associated image does not
|
|
have multiple frames.
|
|
|
|
Pillow cannot in general close and reopen a file, so any access to
|
|
that file needs to be prior to the close.
|
|
|
|
Image Lifecycle
|
|
---------------
|
|
|
|
* ``Image.open()`` Filenames and ``Path`` objects are opened as a file.
|
|
Metadata is read from the open file. The file is left open for further usage.
|
|
|
|
* ``Image.Image.load()`` When the pixel data from the image is
|
|
required, ``load()`` is called. The current frame is read into
|
|
memory. The image can now be used independently of the underlying
|
|
image file.
|
|
|
|
Any Pillow method that creates a new image instance based on another will
|
|
internally call ``load()`` on the original image and then read the data.
|
|
The new image instance will not be associated with the original image file.
|
|
|
|
If a filename or a ``Path`` object was passed to ``Image.open()``, then the
|
|
file object was opened by Pillow and is considered to be used exclusively by
|
|
Pillow. So if the image is a single-frame image, the file will be closed in
|
|
this method after the frame is read. If the image is a multi-frame image,
|
|
(e.g. multipage TIFF and animated GIF) the image file is left open so that
|
|
``Image.Image.seek()`` can load the appropriate frame.
|
|
|
|
* ``Image.Image.close()`` Closes the file and destroys the core image object.
|
|
|
|
The Pillow context manager will also close the file, but will not destroy
|
|
the core image object. e.g.::
|
|
|
|
with Image.open("test.jpg") as img:
|
|
img.load()
|
|
assert img.fp is None
|
|
img.save("test.png")
|
|
|
|
|
|
The lifecycle of a single-frame image is relatively simple. The file must
|
|
remain open until the ``load()`` or ``close()`` function is called or the
|
|
context manager exits.
|
|
|
|
Multi-frame images are more complicated. The ``load()`` method is not
|
|
a terminal method, so it should not close the underlying file. In general,
|
|
Pillow does not know if there are going to be any requests for additional
|
|
data until the caller has explicitly closed the image.
|
|
|
|
|
|
Complications
|
|
-------------
|
|
|
|
* ``TiffImagePlugin`` has some code to pass the underlying file descriptor into
|
|
libtiff (if working on an actual file). Since libtiff closes the file
|
|
descriptor internally, it is duplicated prior to passing it into libtiff.
|
|
|
|
* After a file has been closed, operations that require file access will fail::
|
|
|
|
with open("test.jpg", "rb") as f:
|
|
im5 = Image.open(f)
|
|
im5.load() # FAILS, closed file
|
|
|
|
with Image.open("test.jpg") as im6:
|
|
pass
|
|
im6.load() # FAILS, closed file
|
|
|
|
|
|
Proposed File Handling
|
|
----------------------
|
|
|
|
* ``Image.Image.load()`` should close the image file, unless there are
|
|
multiple frames.
|
|
|
|
* ``Image.Image.seek()`` should never close the image file.
|
|
|
|
* Users of the library should use a context manager or call
|
|
``Image.Image.close()`` on any image opened with a filename or ``Path``
|
|
object to ensure that the underlying file is closed.
|