解决pip install -r requirements.txt安装过程中出现的问题

报错：ERROR: Could not find a version that satisfies the requirement futures (from -r requirements.txt (line 1)) (from versions: none)
ERROR: No matching distribution found for futures (from -r requirements.txt (line 1))

 原因：环境变量改变，可以通过指令查看：

env |grep -i proxy

结果如下：

可以看到不为空值，应该设为空值

 export https_proxy=""

export http_proxy=""

现在就能正常安装了