PIL open（）方法不能与BytesIO一起使用

Question

For some reason, when I try to make an image from a BytesIO steam, it can't identify the image. Here is my code:

from PIL import Image, ImageGrab
from io import BytesIO

i = ImageGrab.grab()
i.resize((1280, 720))
output = BytesIO()
i.save(output, format = "JPEG")
output.flush()
print(isinstance(Image.open(output), Image.Image))

And the stack trace of the error it throws:

Traceback (most recent call last):
  File "C:/Users/Natecat/PycharmProjects/Python/test.py", line 9, in <module>
    print(isinstance(Image.open(output), Image.Image))
  File "C:\Python27\lib\site-packages\PIL\Image.py", line 2126, in open
    % (filename if filename else fp))
IOError: cannot identify image file <_io.BytesIO object at 0x02394DB0>

I am using the Pillow implementation of PIL.

Answer 1

Think of BytesIO as a file object, after you finish writing the image, the file's cursor is at the end of the file, so when Image.open() tries to call output.read() , it immediately gets an EOF.

You need to add a output.seek(0) before passing output to Image.open() .