源代码： Lib/imghdr.py
The imghdr 模块确定文件或字节流中包含的图像类型。
The imghdr 模块定义以下函数：
Tests the image data contained in the file named by filename , and returns a string describing the image type. If optional h is provided, the filename is ignored and h is assumed to contain the byte stream to test.
The following image types are recognized, as listed below with the return value from what() :
| 值 | 图像格式 |
|---|---|
| 'rgb' | SGI ImgLib 文件 |
| 'gif' | GIF 87a 和 89a 文件 |
| 'pbm' | PBM (便携式位图) 文件 |
| 'pgm' | PGM (便携式灰度图) 文件 |
| 'ppm' | PPM (便携式像素图) 文件 |
| 'tiff' | TIFF 文件 |
| 'rast' | Sun 光栅文件 |
| 'xbm' | XBM (X 位图) 文件 |
| 'jpeg' | JPEG data in JFIF or Exif formats |
| 'bmp' | BMP 文件 |
| 'png' | PNG (便携式网络图形) |
New in version 2.5: Exif detection.
You can extend the list of file types imghdr can recognize by appending to this variable:
A list of functions performing the individual tests. Each function takes two arguments: the byte-stream and an open file-like object. When what() is called with a byte-stream, the file-like object will be None .
The test function should return a string describing the image type if the test succeeded, or None if it failed.
范例：
>>> import imghdr >>> imghdr.what('bass.gif') 'gif'
