1.问题记录
执行pip install -r requirements.txt时报下述error:
error: can't find Rust compiler
This package requires Rust >=1.41.0.
Failed building wheel for cryptography
Failed cleaning build dir for cryptography
2.问题解决
(1)安装rust编译器: https://www.rust-lang.org/tools/install
(2)升级pip后重新执行pip install
    $ easy_install pip
    $ pip install -r requirements.txt