File Handling in Pillow¶
When opening a file as an image, Pillow requires a filename,
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
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.
Pathobjects 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.
If a filename or a
Pathobject 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. This is used in the Pillow context manager support. e.g.:
with Image.open('test.jpg') as img: ... # image operations here.
The lifecycle of a single-frame image is relatively simple. The file must
remain open until the
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.
TiffImagePluginhas 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
Pathobject to ensure that the underlying file is closed.