pip 安装 pymysql 报错 OSError: HTTPSConnectionPool

python中连接mysql，需要安装pymysql
安装时报错提示

pip install pymysql

Collecting pymysql
  WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x103288f90>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/4f/52/a115fe175028b058df353c5a3d5290b71514a83f67078a6482cff24d6137/PyMySQL-1.0.2-py3-none-any.whl
  WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x103289ed0>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/4f/52/a115fe175028b058df353c5a3d5290b71514a83f67078a6482cff24d6137/PyMySQL-1.0.2-py3-none-any.whl
  WARNING: Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x10328a790>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/4f/52/a115fe175028b058df353c5a3d5290b71514a83f67078a6482cff24d6137/PyMySQL-1.0.2-py3-none-any.whl
  WARNING: Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x10328bbd0>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/4f/52/a115fe175028b058df353c5a3d5290b71514a83f67078a6482cff24d6137/PyMySQL-1.0.2-py3-none-any.whl
  WARNING: Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x10323a410>: Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known')': /packages/4f/52/a115fe175028b058df353c5a3d5290b71514a83f67078a6482cff24d6137/PyMySQL-1.0.2-py3-none-any.whl
ERROR: Could not install packages due to an OSError: HTTPSConnectionPool(host='files.pythonhosted.org', port=443): Max retries exceeded with url: /packages/4f/52/a115fe175028b058df353c5a3d5290b71514a83f67078a6482cff24d6137/PyMySQL-1.0.2-py3-none-any.whl (Caused by NewConnectionError(': Failed to establish a new connection: [Errno 8] nodename nor servname provided, or not known'))

解决办法：更换下载源

临时指定使用国内的源地址

pip install pymysql -i https://pypi.tuna.tsinghua.edu.cn/simple

更多源地址参考

清华：https://pypi.tuna.tsinghua.edu.cn/simple
阿里云：http://mirrors.aliyun.com/pypi/simple
中国科技大学 https://pypi.mirrors.ustc.edu.cn/simple
华中理工大学：http://pypi.hustunique.com/
山东理工大学：http://pypi.sdutlinux.org/ 
豆瓣：http://pypi.douban.com/simple/