背景
今天在公司安装了Anaconda，准备更换下Anaconda自带的jupyter notebook的主题，但是执行pip install时报TLS/SSL错误。
安装环境
Win7 64位
Anaconda (Python 3.7)，并已将D:\Anaconda3和D:\Anaconda3\Scripts添加到环境变量PATH中。
问题详情
执行以下命令报错：
pip install --upgrade jupyterthemes
错误描述：
pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.
Collecting jupyterthemes
Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by ‘SSLError(“Can’t connect to HTTPS URL because the SSL module is not available.”)’: /simple/jupyterthemes/
Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by ‘SSLError(“Can’t connect to HTTPS URL because the SSL module is not available.”)’: /simple/jupyterthemes/
Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by ‘SSLError(“Can’t connect to HTTPS URL because the SSL module is not available.”)’: /simple/jupyterthemes/
Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by ‘SSLError(“Can’t connect to HTTPS URL because the SSL module is not available.”)’: /simple/jupyterthemes/
Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by ‘SSLError(“Can’t connect to HTTPS URL because the SSL module is not available.”)’: /simple/jupyterthemes/
Could not fetch URL https://pypi.org/simple/jupyterthemes/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host=‘pypi.org’, port=443): Max retries exceeded with url: /simple/jupyterthemes/ (Caused by SSLError(“Can’t connect to HTTPS URL because the SSL module is not available.”)) - skipping
Could not find a version that satisfies the requirement jupyterthemes (from versions: )
No matching distribution found for jupyterthemes
解决方案
最开始在网上搜索同类问题，大都是说python 的ssl模块未安装，从问题描述来看确实也很像，但是他们的问题大多发生在Linux上，而我的是Windows，又联想到Anaconda本来就是一个Python的套件包，包含了许多常用的工具和Python库，不可能犯这种低级错误，所以很可能是环境变量未配置全，导致pip无法找到ssl相关模块。
最终参考之前正常的Anaconda的配置，将"[Anaconda安装目录]\Library\bin"加入PATH后，问题解决。
如下，jupyterthemes安装成功：
