Developing, compiling, testing, releasing

gmic-py is a C/Python binding of C++ which must be compiled or pre-compiled for any target machines in order to work. Third-party frameworks for writing bindings such as Pybind11 or Pyrex have not been used because of the binding’s simplicity.

Any Linux / Mac OS / Unix operating system with Python >= 3.6 (possibly less) should be able to compile the binding without any non-standard Python tooling. 32bit architectures are not supported since Q3 2020, in favor of pure x86_64, but the project used to compile well against the former.

TL;DR building gmic-py on Linux

You can build G’MIC by forcing pip install to build it from a source tarball:

pip install gmic --compile

You can build G’MIC from a Git repository clone. For this run the following lines one by one, deciding on your options:

git clone --depth=1

# For Centos / Redhat / Fedora..:
yum install fftw-devel libpng-devel zlib-devel libgomp libtiff-devel libjpeg-devel wget

# For Ubuntu
sudo apt-get install libfftw3-dev libcurl4-openssl-dev libpng-dev liblz-dev libgomp1 libtiff-dev libjpeg-dev wget

# Download libgmic's preassembled source archive (equates to 2 git clone commands + 2-3 make commands..)
bash build_tools.bash 1_clean_and_regrab_gmic_src

# For building linux-repaired wheels, using the manylinux docker images, run:
bash build_tools.bash 33_build_manylinux # to focus on one version, add eg. 'cp36' as a final parameter
ls wheelhouse/ # here you have .whl files

# For building just a non-repaired debug .so file the current machine:
bash build_tools.bash 2b_compile_debug
ls build/lib* # cd into any directory with a .so file and run python3 in it, to be able to 'import gmic'

# Same but optmimized non-repaired .so file
bash build_tools.bash 2_compile
ls build/lib*

gmic-py development to release lifecycle (overview)

In very short, the G’MIC Python binding per-version lifecycle is as follows: #. grab libgmic’s C++ targetted version #. tune binding code and pytest cases #. compile and test locally #. git push with a tag to trigger optimized releases building and sending to G’MIC’s project

Go to `gmic-py development to release lifecycle (detailed)`_ for more details on the right tooling to use for each step.

Note: Steps 1-3 correspond to the bash build_tools.bash 00_all_steps command.

Github Actions Continuous integration workflows

Looking that the Github project’s Action’s tab or the .github/workflows files, you will notice the following discting workflows:

  • Linux debug (the fastest to yield a result)

  • MacOS optimized

  • Manylinux optimized

  • Manylinux optimized, on Git tag push optimized with release (to

  • MacOS optimized on Git tag push with release (to

All of them leverage build_tools.bash and show the needed package for each OS.

build_tools.bash - a developer’s Swiss army knife

Located in the Git repository’s root, build_tools.bash is used for developing, building and releasing gmic-py.

Before running build_tools.bash, you should install the developer requirements first:

pip install -r dev-requirements.txt

Then, a running the former script without parameters or with --help shows the targeted G’MIC version and the available commands.

Centralized version for development and continuous-integration-based releasing

The targeted G’MIC version is the available version of G’MIC (according to its source archives and pre-releases) for which we are developing a binding and preparing a release. It is stored in the VERSION file (add no trailing character after the version number there!) for use by build_tools.bash, the continuous integration scripts.

Calling build_tools.bash

To call any command just append its name as a first parameter:

$ bash build_tools.bash <the command name>
$ # For example:
$ bash build_tools.bash1_clean_and_regrab_gmic_src # Will grab the libgmic C++ code

Rapid sub-commands overview and explanations

Exhaustive commands documentation will not be covered hereafter. In order to understand them, you should look at their implementations within the bash script and their use within the .github/worfklows/ Github Action continuous integration recipes. In it, one function equates to one command.

  • 00_all_steps: Use this if you are a beginner with build_tools.bash and have time on a Linux machine with a Python virtual environment, it will grab G’MIC’s C++ source, compile, test and bundle it without making any release. More experienced developer in the project will likely run single steps only. This can also be run from a Docker image, although the related Dockerfile now only survives in Git history <>_ because it is used very rarely.

  • 1_clean_and_regrab_gmic_src: download libgmic’s C++ code into the src/ directory (which is emptied beforehand)

  • 11_send_to_pypi: send built wheels (.whl) to using twine

  • 2_compile: compile with optimization (long). On Linux a .so file is generated in the build/ directory.

  • 2b_compile_debug: compile without optimization (fast) and with debug symbols.

  • 20_reformat_all: reformat both Python and C code (note this is not done after compile time in manylinux to avoid crashes). You usually run this by hand before doing a Git commit.

  • 21_check_c_style: using clang-format.

  • 22_reformat_c_style: using clang-format.

  • 23i_install_black_python_formatter: installed a locked version of the black Python formatter and checker.

  • 23_check_python_style: using black.

  • 24_reformat_python_style: using black.

  • 33_build_manylinux: build gmic-py with optimized compiling using the PEP 571 standard for old Linux distributions. This technique nicknamed manylinux ships with a Docker image we use on Github Actions. Rarely run locally because it is super long, but this is safe as it is dockerized. Check for your built wheels in the wheels/ directory.

  • 3_test_compiled_so: runs pytest cases from tests/ onto your build/lib* shared gmic-py library.

  • 3b_test_compiled_so_no_numpy: similar by omitting the Numpy-support test suite.

  • 31_test_compiled_so_filters_io: very long experimental test suite with G’MIC gmic cli command vs gmic-py module output images result comparison.

  • 4_build_wheel: build a .whl wheel without embedding external shared libraries (ie. doing a “repair” step as needed on Linuxes, but not on MacOS or Windows). When run, head over to the build/dist* directory.

  • 5_test_wheel: runs pytest cases over the last built wheel.

Library requirements

gmic-py embeds libgmic C++ library and has the same library needs as the latter. Namely zlib and libpng, optionally libfftw3, libjpeg, libtiff, OpenMP. gmic-py’s file shows the use of the Unix-compatible pkgconfig module, for available libraries detection and toggling in order to run a smooth compilation with you having to tune compile flags at all.

Note that our releases are all built against: zlib, libpng, libopenmp, libtiff, libjpeg, similarly to libgmic releases. Libgmic IS embedded inside the gmic-py binding.

Optimized vs. debugging

For testing and daily development, gmic-py can be compiled faster with no optimization and with debug symbols attached. This is down through a hackish --debug flag. This is what is run through


debug_enabled = "--debug" in sys.argv

For releases, an optimized build is generated, just by omitting the --debug flag.

For debugging segfaults or other situations, you can run gdb python and explore with the gdb command line. You can also use CLion (or any C++ editor), load the C source and Python script of your own using the gmic module, run your Python script in Debug mode or with some blocking input() or other pure-python breakpoing for example, and attach with your C++ IDE to the latest Python process run. Here is a similar very barebone way of debugging with IPython and lldb (or gdb).

On the fly compiling with pip

You can compile automatically through a pip which will run the compiling steps for you, it will download gmic-py’s source from its most stable origin:

pip install --no-binary gmic

Compiling from a git clone

Compiling locally from a Git clone is usually done with GCC/CLang and gets inspiration from libgmic’s own Makefile. There are no special tricks, but Python tools are used best instead of direct compiler calling. build # will need a pip install pkgconfig first

Which is done by build_tools.bash 2_compile or 2b_compile_debug variant as well.

Though you will libgmic’s source first. See the next section instead for doing first things first.

gmic-py development to release lifecycle (detailed)

  1. once for all, install developer’s requirements in a project own virtual environment:

pip install -r dev-requirements.txt
  1. change the targetted G’MIC version number (we follow libgmic’s versioning) in VERSION. build_tools.bash, and the Github Actions workflow files will all rely on this central piece of data!

echo "2.9.1" > VERSION

Note: this version can be overriden on a per-command basis for build_tools.bash by setting the GMIC_VERSION environment variable. Read build_tools.bash code for details.

  1. grab the related libgmic C++ source

bash build_tools.bash 1_clean_and_regrab_gmic_src
  1. edit gmicpy.cpp gmicpy.h the pytest tests/

  2. edit the documentation in docs/ (it gets deployed to on each Git push)

  3. rebuild documentation for previewing:

pip install sphinx # one time only
cd docs/; make html
  1. compile in debug mode

bash build_tools.bash 2b_compile_debug
  1. run few or all unit tests locally

bash build_tools.bash 3_test_compiled_so # for all tests
bash build_tools.bash 3b_test_compiled_so_no_numpy # for all tests, except numpy ones
bash build_tools.bash 3b_test_compiled_so_no_numpy openmp # all tests the name of which matches the *openmp* wildcard
  1. hand test interactively (outside any Python virtual environment, or using an environment with gmic uninstalled)

cd build/lib.linux-x86_64-3.6/
ls # shows
# import gmic
#"sp earth") # etc
  1. check linked shared libraries

cd build/lib.linux-x86_64-3.6/
  1. Git push without any tag to trigger Github Actions for Mac OS and Linux debug and optimized builds, as well as documentation building

git push # (origin master) or any other Github branch
  1. set a Git tag and Git push to trigger the former Github Actions + identical ones optimized with release wheels upload

git tag -a v2.9.1 # In this project, the tag must start with v for releasing
git push # origin master or any other Github branch
  1. look at’s gmic module released contents

  2. test online releases by hand (in a Python environment without gmic installed)

pip install gmic # or gmic==2.9.1 in our case
# import gmic
#"sp earth") # etc
py.test tests/