Working with Matplotlib on OSX

Contents

• Working with Matplotlib on OSX
  • Introduction
  • Short version
    • VirtualEnv
    • Conda
  • Long version
    • PYTHONHOME Function
      • PYTHONHOME Script
      • PythonW Compiler

Introduction

On OSX, two different types of Python Builds exist: a regular build and a framework build. In order to interact correctly with OSX through the native GUI frameworks you need a framework build of Python. At the time of writing the macosx and WXAgg backends require a framework build to function correctly. This can result in issues for a python installation not build as a framework and may also happen in virtual envs and when using (Ana)Conda. From Matplotlib 1.5 onwards the macosx backend checks that a framework build is available and fails if a non framework build is found. WX has a similar check build in.

Without this check a partially functional figure is created. Among the issues with it is that it is produced in the background and cannot be put in front of any other window. Several solutions and work arounds exist see below.

Short version

VirtualEnv

If you are on Python 3, use venv instead of virtualenv:

python -m venv my-virtualenv
source my-virtualenv/bin/activate

Otherwise you will need one of the workarounds below.

Conda

The default python provided in (Ana)Conda is not a framework build. However, the Conda developers have made it easy to install a framework build in both the main environment and in Conda envs. To use this install python.app conda install python.app and use pythonw rather than python

Long version

Unfortunately virtualenv creates a non framework build even if created from a framework build of Python. As documented above you can use venv as an alternative on Python 3.

The issue has been reported on the virtualenv bug tracker here and here

Until this is fixed, one of the following workarounds can be used:

PYTHONHOME Function

The best known work around is to use the non virtualenv python along with the PYTHONHOME environment variable. This can be done by defining a function in your .bashrc using

function frameworkpython {
    if [[ ! -z "$VIRTUAL_ENV" ]]; then
        PYTHONHOME=$VIRTUAL_ENV /usr/local/bin/python "$@"
    else
        /usr/local/bin/python "$@"
    fi
}

This function can then be used in all of your virtualenvs without having to fix every single one of them.

With this in place you can run frameworkpython to get an interactive framework build within the virtualenv. To run a script you can do frameworkpython test.py where test.py is a script that requires a framework build. To run an interactive IPython session with the framework build within the virtual environment you can do frameworkpython -m IPython

PYTHONHOME Script

An alternative work around borrowed from the WX wiki, is to use the non virtualenv python along with the PYTHONHOME environment variable. This can be implemented in a script as below. To use this modify PYVER and PATHTOPYTHON and put the script in the virtualenv bin directory i.e. PATHTOVENV/bin/frameworkpython

#!/bin/bash

# what real Python executable to use
PYVER=2.7
PATHTOPYTHON=/usr/local/bin/
PYTHON=${PATHTOPYTHON}python${PYVER}

# find the root of the virtualenv, it should be the parent of the dir this script is in
ENV=`$PYTHON -c "import os; print(os.path.abspath(os.path.join(os.path.dirname(\"$0\"), '..')))"`

# now run Python with the virtualenv set as Python's HOME
export PYTHONHOME=$ENV
exec $PYTHON "$@"

With this in place you can run frameworkpython as above but will need to add this script to every virtualenv

PythonW Compiler

In addition virtualenv-pythonw-osx provides an alternative workaround which may be used to solve the issue.