Package python is not available, but is referred to by another package

[spock]

When building the image locally, got this error:

Step 19/61 : RUN apt-get -y install python build-essential libglib2.0-dev libpixman-1-dev ninja-build
 ---> Running in d3817f7d3c0a
Reading package lists...
Building dependency tree...
Reading state information...
Package python is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  python-is-python3 2to3