# Installation procedure on MacOSX

## Install Python3:

To install pyFAI on an Apple computer you will need a scientific Python3 stack. MacOSX provides by default Python2.7, you will need to install a recent version of Python3 (3.5 at least, 3.7 recommanded but newer version should be OK). Those distribution are available as dmg images from: https://www.python.org/downloads/mac-osx/

After downloading, move the app into the Applications folder.

## Using a virtual environment:

    python3 -m venv pyfai
    source pyfai/bin/activate
    pip install pyFAI[full]

If you get an error about the local “UTF-8”, try to:

    export LC_ALL=C

Before the installation.

## Installation from sources

Get the sources from Github:

    wget https://github.com/silx-kit/pyFAI/archive/master.zip
    unzip master.zip
    cd pyFAI-master
    pip install -r requirements.txt
    python setup.py build bdist_wheel
    pip install --find-links=dist --pre --no-index --upgrade pyFAI

### About OpenMP

OpenMP is a way to write multi-threaded code, running on multiple processors simultaneously. PyFAI makes heavy use of OpenMP, but there is an issue with recent versions of MacOSX (>v10.6) where the default compiler of Apple, Xcode, dropped the support for OpenMP.

There are two ways to compile pyFAI on MacOSX:

- Using Xcode and de-activating OpenMP in pyFAI
- Using another compiler which supports OpenMP

### Using Xcode

To build pyFAI from sources, a C-compiler is needed. On an Apple computer, the default compiler is Xcode, and it is available for free on the AppStore. As pyFAI will deactivate OpenMP on apple computer, for this it needs to regenerate all Cython files without OpenMP.

The absence of OpenMP is mitigated on Apple computer by the support of OpenCL which provied parallel intgeration.

### Using gcc or clang

If you want to keep the OpenMP feature (which makes the processing slightly faster), the alternative is to install another compiler like gcc or clang on your Apple computer.

    CC=gcc python setup.py build --openmp
    python setup.py bdist_wheel
    pip install --find-links=dist/ --pre --no-index --upgrade pyFAI

Nota: The usage of “python setup.py install” is now deprecated. It causes much more trouble as there is no installed file tracking, hence no way to properly un-install a package.