试图为python安装lxml，“无法在库libxml2中找到函数xmlCheckVersion。”

Question

我正在尝试使用pip为python安装lxml。我尝试了sudo pip install lxml和sudo pip install lxml这两个都给出了错误：

Could not find function xmlCheckVersion in library libxml2. Is libxml2 installed?
    Perhaps try: xcode-select --install
    *********************************************************************************
    error: command 'cc' failed with exit status 1

不知道这里发生了什么。谁是Xcode参与？任何指针都会非常感激。