# Installation procedure on Windows

PyFAI is a Python library. Even if you are only interested in some tool like pyFAI-calib or pyFAI-integrate, you need to install the complete library (for now). This is usually performed in 3 steps:

1. install Python,
2. install the scientific Python stack
3. install pyFAI itself.

## Get Python

Unlike on Unix computers, Python is not available by default on Windows computers. We recommend you to install the 64 bit version of Python, preferably the latest 64 bits version from the 3.6 series. Python 2.7 and 3.4 are no more supported since pyFAI v0.19. Python 2.6, 3.2 and 3.3 are no more supported since pyFAI v0.12.

The 64 bits version is strongly advised if your hardware and operating system supports it, as the 32 bits versions is limited to 2 GB of memory, hence unable to treat large images (like 4096 x 4096). The test suite is not passing on Windows 32 bits due to the limited amount of memory available to the Python process, nevertheless, pyFAI is running on Windows 32 bits (but not as well).

Alternative Scientific Python stacks exists, like Enthought Python Distribution , Anaconda, WinPython. They all offer most of the scientific packages already installed which makes the installation of dependencies much easier. On the other hand, they all offer different packaging system and we cannot support all of them. Moreover, distribution from Enthought and Continuum are not free so you should be able to get support from those companies.

Nota: any flavor of those Python distribution is probably incompatible with any other due to change in compiler or Python compilation options. Mixing them is really looking for trouble, hence strongly discouraged. If you want an advice on which scientific python distribution for Windows to use, I would recommend WinPython.

## Install PIP

PIP is the package management system for Python, it connects to the Python Package Index, download and install software packages from there.

PIP has revolutionize the way Python libraries are installed as it is able to select the right build for your system, or compile them from the sources, which could be extremely tricky otherwise. If you installed Python compatible with pyFAI (3.5 or newer), PIP is already installed. If pip is not yet installed on your system, download get_pip.py and run it:

    python get-pip.py

Assuming python.exe is already in your PATH.

Nota: Because PIP connects to the network, the http_proxy and https_proxy environment variable may need to be set-up properly. At ESRF, this is no more needed.

## Install pyFAI via PIP

    pip install pyFAI[gui] --upgrade

This will install:

- NumPy
- SciPy
- matplotlib
- FabIO
- h5py
- silx
- h5py
- PyQt5

### Using Christoph Gohlke repository

Christoph Gohlke is a researcher at Laboratory for Fluorescence Dynamics, University of California, Irvine. He is maintaining a large repository Python extension (actually, all we need :) for Windows. Check twice the Python version and the Windows version (win32 or win_amd64) before downloading.

Moreover the libraries he provides are linked against the MKL library from Intel which makes his packages faster then what you would get by simply recompiling them.

Christoph now provides packages as wheels. To install them, download the wheels and use PIP:

    pip install numpy*.whl

Alternatively, you can use the wheelhouse of the silx project:

    pip install --trusted-host www.silx.org --find-links http://www.silx.org/pub/wheelhouse/ numpy scipy matplotlib fabio PyQt5

## Install pyFAI from sources

The sources of pyFAI are available at https://github.com/silx-kit/pyFAI/releases the development is performed on https://github.com/silx-kit/pyFAI

In addition to the Python interpreter, you will need *the* C compiler compatible with your Python interpreter.

To upgrade the C-code in pyFAI, one needs in addition Cython:

    pip install -r requirements.txt --upgrade
    python setup.py bdist_wheel
    pip install --upgrade --pre --no-index --find-links dist/ pyFAI

## Troubleshooting

This section contains some tips on windows.

### Side-by-side error

When starting pyFAI you get a side-by-side error like:

    ImportError: DLL load failed: The application has failed to start because its
    side-by-side configuration is incorrect. Please see the application event log or
    use the command-line sxstrace.exe tool for more detail.

This means you are using a version of pyFAI which was compiled using the MSVC compiler (maybe not on your computer) but the Microsoft Visual C++ Redistributable Package is missing.