Collecting xlwt

  Could not fetch URL https://pypi.python.org/simple/xlwt/: There was a problem confirming the ssl certificate: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:661) - skipping

  Could not find a version that satisfies the requirement xlwt (from versions: )

No matching distribution found for xlwt

是因为低版本的python 没有使用SSL连接， 我们在安装的请求参数添加如下选项  --trusted-host pypi.python.org ，就可以安装成功