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/Doc/library/imghdr.rst

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 1
 2:mod:`imghdr` --- Determine the type of an image
 3================================================
 4
 5.. module:: imghdr
 6   :synopsis: Determine the type of image contained in a file or byte stream.
 7
 8
 9The :mod:`imghdr` module determines the type of image contained in a file or
10byte stream.
11
12The :mod:`imghdr` module defines the following function:
13
14
15.. function:: what(filename[, h])
16
17   Tests the image data contained in the file named by *filename*, and returns a
18   string describing the image type.  If optional *h* is provided, the *filename*
19   is ignored and *h* is assumed to contain the byte stream to test.
20
21The following image types are recognized, as listed below with the return value
22from :func:`what`:
23
24+------------+-----------------------------------+
25| Value      | Image format                      |
26+============+===================================+
27| ``'rgb'``  | SGI ImgLib Files                  |
28+------------+-----------------------------------+
29| ``'gif'``  | GIF 87a and 89a Files             |
30+------------+-----------------------------------+
31| ``'pbm'``  | Portable Bitmap Files             |
32+------------+-----------------------------------+
33| ``'pgm'``  | Portable Graymap Files            |
34+------------+-----------------------------------+
35| ``'ppm'``  | Portable Pixmap Files             |
36+------------+-----------------------------------+
37| ``'tiff'`` | TIFF Files                        |
38+------------+-----------------------------------+
39| ``'rast'`` | Sun Raster Files                  |
40+------------+-----------------------------------+
41| ``'xbm'``  | X Bitmap Files                    |
42+------------+-----------------------------------+
43| ``'jpeg'`` | JPEG data in JFIF or Exif formats |
44+------------+-----------------------------------+
45| ``'bmp'``  | BMP files                         |
46+------------+-----------------------------------+
47| ``'png'``  | Portable Network Graphics         |
48+------------+-----------------------------------+
49
50.. versionadded:: 2.5
51   Exif detection.
52
53You can extend the list of file types :mod:`imghdr` can recognize by appending
54to this variable:
55
56
57.. data:: tests
58
59   A list of functions performing the individual tests.  Each function takes two
60   arguments: the byte-stream and an open file-like object. When :func:`what` is
61   called with a byte-stream, the file-like object will be ``None``.
62
63   The test function should return a string describing the image type if the test
64   succeeded, or ``None`` if it failed.
65
66Example::
67
68   >>> import imghdr
69   >>> imghdr.what('/tmp/bass.gif')
70   'gif'
71