无法使用 pip (ubuntu) [pip 配置了需要 TLS/SSL 的位置，但是 Python 中的 ssl 模块不可用。]

$ sudo pip install numpy    # or anything else

错误：

The directory '/home/user/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag. (tried sudo -H, the rest errors persist)  
pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.    
Collecting numpy  
  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/numpy/  
pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.  
Could not fetch URL https://pypi.org/simple/pip/: There was a problem confirming the ssl certificate: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/pip/ (Caused by SSLError("Can't connect to HTTPS URL because the SSL module is not available.")) - skipping  

$ python -V
Python 3.7.3  
$ pip -V
pip 19.0.3 from /usr/local/lib/python3.7/site-packages/pip (python 3.7)
$ whereis pip
pip: /usr/local/bin/pip2.7 /usr/local/bin/pip3.7 /usr/local/bin/pip /usr/local/bin/pip3.6  

pip3.6 出现在：

$ sudo su
$ update-alternatives --install /usr/bin/python python /usr/bin/python3 1

在 anaconda 环境中，pip 工作正常。

以安全的方式删除与 python 相关的东西——不破坏系统，并正确地重新安装东西，是一个更可取的解决方案吗？以及如何做到这一点？

我知道有很多类似的问题，但是我尝试了很多东西（显然，我搞砸了一些东西）并且我没有解决问题。

谢谢！