Python：检查上传的文件是否为jpg [英] Python: Check if uploaded file is jpg

问题描述

如何检查用户上传的文件是否是真正的Python文件（Google App Engine）？

How can I check if a file uploaded by a user is a real jpg file in Python (Google App Engine)?

这是我现在得到的：

脚本通过HTML Form Post接收图片，并由以下代码处理

Script receives image via HTML Form Post and is processed by the following code

...
incomming_image = self.request.get("img")
image = db.Blob(incomming_image)
...

我找到了mimetypes.guess_type，但它不适用于我。

I found mimetypes.guess_type, but it does not work for me.

推荐答案

如果您需要的不仅仅是查看扩展，还有一种方法是读取JPEG标头，并检查它是否与有效数据匹配。格式为：

If you need more than looking at extension, one way would be to read the JPEG header, and check that it matches valid data. The format for this is:

Start Marker  | JFIF Marker | Header Length | Identifier
0xff, 0xd8    | 0xff, 0xe0  |    2-bytes    | "JFIF\0"

所以一个快速识别器是：

so a quick recogniser would be:

def is_jpg(filename):
    data = open(filename,'rb').read(11)
    if data[:4] != '\xff\xd8\xff\xe0': return False
    if data[6:] != 'JFIF\0': return False
    return True

然而，这并不能捕捉到任何不正确的数据。如果您想要更强大的检查，可以尝试使用 PIL 加载。例如：

However this won't catch any bad data in the body. If you want a more robust check, you could try loading it with PIL. eg:

from PIL import Image
def is_jpg(filename):
    try:
        i=Image.open(filename)
        return i.format =='JPEG'
    except IOError:
        return False

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