安装中曾遇到过的问题
cffi.ffiplatform.VerificationError: importing 'C:\\Python27\\lib\\site-packages\\cryptogr\_Cryptography_cffi_48bbf0ebx93c91939.pyd': DLL load failed: The operating system cannot
出现这个问题是因为为安装过程中需要libeay32.dll,ssleay32.dll
参考: getting-error-dll-load-failed-the-operating-system-cannot-run-1-python-2-7