我在OS X 10.11上的virtualenv中安装了带有pip的scrapy。当它安装加密技术时，它说：
building '_openssl' extension
cc -fno-strict-aliasing -fno-common -dynamic -arch i386 -arch x86_64 -g -Os -pipe -fno-common -fno-strict-aliasing -fwrapv -DENABLE_DTRACE -DMACOSX -DNDEBUG -Wall -Wstrict-prototypes -Wshorten-64-to-32 -DNDEBUG -g -fwrapv -Os -Wall -Wstrict-prototypes -DENABLE_DTRACE -arch i386 -arch x86_64 -pipe -I/System/Library/Frameworks/Python.framework/Versions/2.7/include/python2.7 -c build/temp.macosx-10.11-intel-2.7/_openssl.c -o build/temp.macosx-10.11-intel-2.7/build/temp.macosx-10.11-intel-2.7/_openssl.o
build/temp.macosx-10.11-intel-2.7/_openssl.c:423:10: fatal error: 'openssl/e_os2.h' file not found
#include <openssl/e_os2.h>
^
1 error generated.
error: command 'cc' failed with exit status 1
Command "/Users/Kris/Workspace/env/scrapy/bin/python -c "import setuptools, tokenize;__file__='/private/var/folders/wx/jm7lxhps3n7484zl4gv9s3180000gn/T/pip-build-2rJYgI/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('rn', 'n'), __file__, 'exec'))" install --record /var/folders/wx/jm7lxhps3n7484zl4gv9s3180000gn/T/pip-nXp2mE-record/install-record.txt --single-version-externally-managed --compile --install-headers /Users/Kris/Workspace/env/scrapy/include/site/python2.7/cryptography" failed with error code 1 in /private/var/folders/wx/jm7lxhps3n7484zl4gv9s3180000gn/T/pip-build-2rJYgI/cryptography
有什么建议可以帮我解决吗
顺便说一句，当我在没有virtualenv的情况下安装scrapy时，一切都很顺利。
pip install --upgrade pip
可能有助于