我正在通过魔杖导入ImageMagick：from wand.image import Image
然后我用它来从图像中获取数据：
try :
with Image(filename='./my_image.png') as img:
sys.stderr.write('SHA-256 message digest for the image pixel stream : ' + img.signature + '\n')
except :
print("Oops! ",sys.exc_info()[0]," occured.")
但是图像格式错误（this one for example），异常无法正确处理，脚本崩溃并显示以下消息：
python：../../magick/quantum.c:216：DestroyQuantumInfo：断言'quantum_info！=（QuantumInfo *）NULL'失败。
Here is the doc about Wand Image signature
为什么异常处理不正确？
我使用的ImageMagick版本（我想这是我使用的Ubuntu 18.04.2 LTS中的默认版本）：
$ identify --version
Version: ImageMagick 6.9.7-4 Q16 x86_64 20170114 http://www.imagemagick.org
Copyright: © 1999-2017 ImageMagick Studio LLC
License: http://www.imagemagick.org/script/license.php
Features: Cipher DPC Modules OpenMP
Delegates (built-in): bzlib djvu fftw fontconfig freetype jbig jng jpeg lcms lqr ltdl lzma openexr pangocairo png tiff wmf x xml zlib
如评论中所建议，我正在寻找ImageMagick错误：
$ identify -debug All line-numbers.png
2019-05-31T16:20:42+02:00 0:00.000 0.000u 6.9.7 Configure identify-im6.q16[30840]: utility.c/ExpandFilenames/940/Configure
Command line: identify {-debug} {All} {line-numbers.png}
2019-05-31T16:20:42+02:00 0:00.000 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/usr/share/ImageMagick-6/coder.xml"
2019-05-31T16:20:42+02:00 0:00.000 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/usr/lib/x86_64-linux-gnu/ImageMagick-6.9.7//config-Q16/coder.xml"
2019-05-31T16:20:42+02:00 0:00.000 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/etc/ImageMagick-6/coder.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/usr/share/doc/imagemagick-6-common/htmlcoder.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/home/username/.config/ImageMagick/coder.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/home/username/.magick/coder.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: coder.c/LoadCoderCache/826/Configure
Loading coder configuration file "/etc/ImageMagick-6/coder.xml" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Module identify-im6.q16[30840]: module.c/OpenModule/1288/Module
Searching for module "PNG" using filename "png.la"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Module identify-im6.q16[30840]: module.c/GetMagickModulePath/558/Module
Searching for coder module file "png.la" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Module identify-im6.q16[30840]: module.c/OpenModule/1297/Module
Opening module at path "/usr/lib/x86_64-linux-gnu/ImageMagick-6.9.7//modules-Q16/coders/png.la"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Module identify-im6.q16[30840]: module.c/OpenModule/1324/Module
Method "RegisterPNGImage" in module "PNG" at address 0x7fac6c16f1c0
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Module identify-im6.q16[30840]: module.c/OpenModule/1338/Module
Method "UnregisterPNGImage" in module "PNG" at address 0x7fac6c16f770
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Policy identify-im6.q16[30840]: policy.c/IsRightsAuthorized/580/Policy
Domain: Path; rights=Read; pattern="line-numbers.png" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Blob identify-im6.q16[30840]: blob.c/OpenBlob/2593/Blob
read 3 magic header bytes
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/usr/share/ImageMagick-6/magic.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/usr/lib/x86_64-linux-gnu/ImageMagick-6.9.7//config-Q16/magic.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/etc/ImageMagick-6/magic.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/usr/share/doc/imagemagick-6-common/htmlmagic.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/home/username/.config/ImageMagick/magic.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: configure.c/GetConfigureOptions/685/Configure
Searching for configure file: "/home/username/.magick/magic.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: magic.c/LoadMagicCache/794/Configure
Loading magic configure file "/etc/ImageMagick-6/magic.xml" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Policy identify-im6.q16[30840]: policy.c/IsRightsAuthorized/580/Policy
Domain: Coder; rights=Read; pattern="PNG" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Policy identify-im6.q16[30840]: policy.c/IsRightsAuthorized/580/Policy
Domain: Path; rights=Read; pattern="line-numbers.png" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Blob identify-im6.q16[30840]: blob.c/OpenBlob/2593/Blob
read 3 magic header bytes
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Coder identify-im6.q16[30840]: png.c/ReadPNGImage/3940/Coder
Enter ReadPNGImage()
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Policy identify-im6.q16[30840]: policy.c/IsRightsAuthorized/580/Policy
Domain: Path; rights=Read; pattern="line-numbers.png" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Blob identify-im6.q16[30840]: blob.c/OpenBlob/2593/Blob
read 3 magic header bytes
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Coder identify-im6.q16[30840]: png.c/ReadOnePNGImage/2042/Coder
Enter ReadOnePNGImage()
IM version = 6.9.7-4
Libpng version = 1.6.34
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Coder identify-im6.q16[30840]: png.c/ReadOnePNGImage/2055/Coder
Zlib version = 1.2.11
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Coder identify-im6.q16[30840]: png.c/ReadOnePNGImage/2085/Coder
Before reading:
image->matte=0
image->rendering_intent=2
image->colorspace=13
image->gamma=0.454545
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Coder identify-im6.q16[30840]: png.c/MagickPNGWarningHandler/1651/Coder
libpng-1.6.34 warning: Image height exceeds user limit in IHDR
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/usr/share/ImageMagick-6/locale.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/usr/lib/x86_64-linux-gnu/ImageMagick-6.9.7//config-Q16/locale.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/etc/ImageMagick-6/locale.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/usr/share/doc/imagemagick-6-common/htmllocale.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/home/username/.config/ImageMagick/locale.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/home/username/.magick/locale.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: locale.c/LoadLocaleCache/1177/Configure
Loading locale configure file "/usr/share/ImageMagick-6/locale.xml" ...
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/usr/share/ImageMagick-6/english.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/usr/lib/x86_64-linux-gnu/ImageMagick-6.9.7//config-Q16/english.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/etc/ImageMagick-6/english.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/usr/share/doc/imagemagick-6-common/htmlenglish.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/home/username/.config/ImageMagick/english.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Locale identify-im6.q16[30840]: locale.c/GetLocaleOptions/824/Locale
Searching for locale file: "/home/username/.magick/english.xml"
2019-05-31T16:20:42+02:00 0:00.010 0.000u 6.9.7 Configure identify-im6.q16[30840]: locale.c/LoadLocaleCache/1177/Configure
Loading locale configure file "/usr/share/ImageMagick-6/english.xml" ...
2019-05-31T16:20:42+02:00 0:00.020 0.000u 6.9.7 Exception identify-im6.q16[30840]: png.c/MagickPNGWarningHandler/1654/Exception
Image height exceeds user limit in IHDR `line-numbers.png'
2019-05-31T16:20:42+02:00 0:00.020 0.000u 6.9.7 Coder identify-im6.q16[30840]: png.c/MagickPNGErrorHandler/1625/Coder
libpng-1.6.34 error: Invalid IHDR data
2019-05-31T16:20:42+02:00 0:00.020 0.000u 6.9.7 Exception identify-im6.q16[30840]: png.c/MagickPNGErrorHandler/1628/Exception
Invalid IHDR data `line-numbers.png'
identify: ../../magick/quantum.c :216 : DestroyQuantumInfo: l'assertion « quantum_info != (QuantumInfo *) NULL » a échoué.
Abandon