Trouble installing the `mindeps` tool

[sschuberth]

First of all, I'm not a Python guy, so sorry if I'm asking stupid questions 😉 I'm looking at using this tool in the ORT Analyzer to list a Python project's (no matter whether defined by a setup.py or a requirements.txt) transitive dependencies and their metadata without actually building the Python project.

The mindeps CLI seems to be suitable for that, but I'm having trouble installing it. I tried this on Ubuntu 18.04 LTS with both Python 2.7 and Python 3.6, but in both cases I'm getting resolver 0.2.1 does not provide the extra 'mindeps':

$ pip install resolver[mindeps]
WARNING: pip is being invoked by an old script wrapper. This will fail in a future version of pip.
Please see https://github.com/pypa/pip/issues/5599 for advice on fixing the underlying issue.
To avoid this problem you can invoke Python with '-m pip' instead of running pip directly.
DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Python 2 support in pip can be found at https://pip.pypa.io/en/latest/development/release-process/#python-2-support pip 21.0 will remove support for this functionality.
Defaulting to user installation because normal site-packages is not writeable
Requirement already satisfied: resolver[mindeps] in /home/user/.local/lib/python2.7/site-packages (0.2.1)
  WARNING: resolver 0.2.1 does not provide the extra 'mindeps'

$ pip3 install resolver[mindeps]
Collecting resolver[mindeps]
  resolver 0.2.1 does not provide the extra 'mindeps'
Installing collected packages: resolver
Successfully installed resolver-0.2.1

Any hints how to install the mindeps CLI porperly?