unable to locate package python3-virtualenv

It seems that it cannot install python3-virutalenv because it doesn't exist (raspberry pi docker image).
It is in the Ubuntu repository though.

I added RUN apt search virtualenv into the dockerfile, seems that python-virtualenv should be used instead?

Sorting...
Full Text Search...
dh-virtualenv/trusty 0.6-1 all
  wrap and build python packages using virtualenv

python-tox/trusty-updates 1.6.0-1ubuntu1 all
  virtualenv-based automation of test activities

python-virtualenv/trusty-updates 1.11.4-1ubuntu1 all
  Python virtual environment creator

virtualenv-clone/trusty 0.2.4-1 all
  script for cloning a non-relocatable virtualenv

virtualenvwrapper/trusty 4.1.1-1 all
  extension to virtualenv for managing multiple virtual Python environments

I fixed the install_deb_packages but now it aborted instead of installing the files (like it'd press n instead of y)
This was because I had a separate command and adding -y fixed that.

The pip injstallation script is completely messed up, too.

1. It uses python3.4
2. The wrong get-pip script is downloaded.

Inspect the Dockerfile's package-installation commands, the install_deb_packages logic, and the pip installation script first. Reproduce the Raspberry Pi image build and verify that the virtualenv package, apt installation, and pip setup complete successfully with the intended Python version and script.