error-externally-managed-environment-every-time-i-use-pip-3

 The proper way to install Python libraries and applications is to install them in a Python virtual environment whenever possible (the exceptions to this rule are quite rare).

As indicated in the error message, there are two commons solutions to achieve this. Either by using a tool that creates a virtual environment for you or by creating a virtual environment directly yourself.

If what you are trying to install is an application then a strong recommendation is to use a tool like pipx. pipx is available for installation as system package on Debian systems and Debian-based systems such as 

Ubuntu:

apt install pipx
pipx install some-python-application

To create a virtual environment yourself you can use Python's venv:

python -m venv my-venv
my-venv/bin/pip install some-python-library

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But if you still decide that you really want to install packages "system-wide" and risk breaking your system, then there are a couple of solutions:

• use pip's argument --break-system-packages,
• add following lines to ~/.config/pip/pip.conf:

[global]
break-system-packages = true