qivenv: virtualenv meets worktree

General

Main goal: make it easy to work with Python code inside a worktree, i.e avoid having to manually set PYTHONPATH and other environment variables.

We’ll use pip and virtualenv because they are becoming the standard to deal with this kind of issues.

More precisely:

  • Handle 3rd-party libraries

  • Handle code that is inside a worktree, which means it’s possible

    to use ‘import foo’ and directly use the code from <worktree>/foo, without having to write a setup.py

  • Handle python extensions written in C++ depending one one or more qibuild CMake projects.

  • Handle C++ code that embeds a Python interpreter and loads Python extensions.

3rd party libraries

This is useful for instance in qidoc, to specify the sphinx version and its deps, or the tools in spinxcontrib, and so on.

This is also useful for whatever Python project.

Solution

  • A requirements.txt (as usual for pip)
  • A hidden virtualenv in .qi/venv automatically created and activated.

For instance, for qidoc, we read the requirements.txt from the templates repo if it exists and use a virtualenv in .qi/venv/qidoc

Python code inside worktree

  • We’ll keep the qiproject.xml syntax
<qiproject version="3">
  <pyproject name="foo" />
</qiproject>
  • By default, name is read from setup.py if it exists
  • By default, list of deps is read from requirements.txt if it exists
  • The virtualenv is in <worktree>/.qi/venv/<name> The tool automatically add the paths of the python projects to <worktree>.qi/venv/<name>/lib/site-packages/qivenv.pth

Python that depends on C++

  • Exactly the same thing, except that we add <build>/sdk/lib/python<version>/site-pacakges> to the .pth file
  • We also do the required magic in CMake so that setting PATH, LD_LIBRARY_PATH or DYLD_LIBRARY_PATH is not necessary, OR we generate a python wrapper that does this.

Embedded Python interpreter in C++

Again, the same thing, but we use virtualenv --python=${PYTHON_EXECUTABLE}, wher PYTHON_EXECUTABLE is found by CMake. So if you are using Python from your system, nothing changes, and if you are using Python from a toolchain, you use it in the virtualenv.

Command line API

  • qivenv list : list the available virtualenvs in the worktree
  • qivenv add <name> [-c config]: add a new virtualenv to the worktree
  • qivenv rm <name>: remove a virtualenv from the worktree
  • qivenv use <name>: use the given virtualenv

Examples:

Running py.test

I want to run py.test on the foo project that depends on the bar project.

  • In foo/requirements.txt I add:
pytest
  • Then I run
$ qivenv use default

Using some Python extension that depends on C++ code

$ qibuild configure -c <config> myext
$ qivenv add <config>
$ qivenv use <config>

$ python
>>> import myext
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