在枕头文件处理¶

When opening a file as an image, Pillow requires a filename, pathlib.Path 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.

以下都是等价:

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.

枕头一般不能关闭并重新打开一个文件，因此该文件需要的任何访问之前结束前。

图片生命周期¶

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.

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. 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 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.

并发症¶

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

建议文件处理¶

Image.Image.load() should close the image file, unless there are multiple frames.
Image.Image.seek（） 都不要关闭图像文件。
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.