Não é possível usar pip (ubuntu) [pip está configurado com locais que exigem TLS/SSL, porém o módulo ssl em Python não está disponível. ]

$ sudo pip install numpy    # or anything else

erro:

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 apareceu depois:

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

Em ambientes anaconda, o pip funciona bem.

A exclusão de coisas relacionadas ao python, em uma extensão segura - sem quebrar o sistema e reinstalar as coisas corretamente, é uma solução preferível? E como fazê-lo?

Eu sei que existem muitas perguntas semelhantes, mas já tentei muitas coisas (obviamente, estraguei alguma coisa) e não consegui resolver o problema.

Obrigado!