前言：同学们在用pip install的时候，可能会遇到MemoryError的问题
报错如下，看最后一行的memory error关键字：
报错的原因大致如下：（详细细节可以查看此处）
**This error is coming up because, it seems, pip's caching mechanism is trying to read the entire file into memory before caching it… which poses a problem in a limited-memory environment, as matplotlib is ~50mb.
** 解决办法：加个参数即可：
pip --no-cache-dir install pyspark
