执行
export C_INCLUDE_PATH=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/usr/include/libxml2:$C_INCLUDE_PATH
Yosemite中pip安装libxml编译失败
原文：http://www.cnblogs.com/portrayer/p/4101625.html
