==============

MPI for Python

This package provides Python bindings for the Message Passing Interface (MPI_) standard. It is implemented on top of the MPI specification and exposes an API which grounds on the standard MPI-2 C++ bindings.

.. _MPI: https://www.mpi-forum.org

Features

This package supports:

• Convenient communication of any picklable Python object

  • point-to-point (send & receive)
  • collective (broadcast, scatter & gather, reductions)

• Fast communication of Python object exposing the Python buffer interface (NumPy arrays, builtin bytes/string/array objects)

  • point-to-point (blocking/nonblocking/persistent send & receive)
  • collective (broadcast, block/vector scatter & gather, reductions)

• Process groups and communication domains

  • creation of new intra/inter communicators
  • creation/query of Cartesian & graph topologies

• Parallel input/output:

  • read & write
  • blocking/nonblocking & collective/noncollective
  • individual/shared file pointers & explicit offset

• Dynamic process management

  • spawn & spawn multiple
  • accept/connect
  • name publishing & lookup

• One-sided operations

  • remote memory access (put, get, accumulate)
  • passive target synchronization (start/complete & post/wait)
  • active target synchronization (lock & unlock)

Install

Wheel packages

The mpi4py project builds and publishes binary wheels able to run in a variety of:

• operating systems: Linux, macOS, Windows;
• processor architectures: AMD64, ARM64;
• MPI implementations: MPICH, Open MPI, MVAPICH, Intel MPI, HPE Cray MPICH, Microsoft MPI;
• Python implementations: CPython, PyPy.

.. _MPICH: https://mpich.org .. _Open MPI: https://open-mpi.org .. _MVAPICH: https://mvapich.cse.ohio-state.edu .. _HPE Cray MPICH: https://cpe.ext.hpe.com/docs/latest/mpt/mpich/ .. _NVIDIA HPC-X: https://developer.nvidia.com/networking/hpc-x .. _Intel MPI: https://software.intel.com/intel-mpi-library .. _Microsoft MPI: https://learn.microsoft.com/message-passing-interface/microsoft-mpi

These mpi4py wheels are distributed via the Python Package Index (PyPI <https://pypi.org/project/mpi4py/>) and can be installed with Python package managers like pip:

.. code:: sh

python -m pip install mpi4py

.. _pip: https://pip.pypa.io

The mpi4py wheels can be installed in standard Python virtual environments. The MPI runtime can be provided by other wheels installed in the same virtual environment.

.. tip::

Intel publishes production-grade Intel MPI wheels <impi-rt-wheels_>_ for Linux (x86_64) and Windows (AMD64). mpi4py and MPI wheels can be installed side by side to get a ready-to-use Python+MPI environment:

.. code:: sh

  python -m pip install mpi4py impi-rt

.. _impi-rt-wheels: https://pypi.org/project/impi-rt/#files

.. tip::

The mpi4py project publishes MPICH wheels <mpich-wheels_>_ and Open MPI wheels <openmpi-wheels_>_ for Linux (x8664/aarch64) and macOS (arm64/x8664). mpi4py and MPI wheels can be installed side by side to get a ready-to-use Python+MPI environment:

.. code:: sh

  python -m pip install mpi4py mpich    # for MPICH
  python -m pip install mpi4py openmpi  # for Open MPI

.. _mpich-wheels: https://pypi.org/project/mpich/#files .. _openmpi-wheels: https://pypi.org/project/openmpi/#files

.. warning::

  The MPI wheels are distributed with special focus on ease of
  use, convenience, compatibility, and interoperability. The Linux
  wheels are built in somewhat constrained environments with
  relatively dated Linux distributions (`manylinux`_ container
  images). Therefore, they may lack support for features like GPU
  awareness (CUDA/ROCm) and C++/Fortran bindings. In production
  scenarios, it is recommended to use external (either
  custom-built or system-provided) MPI installations.

  .. _manylinux: https://github.com/pypa/manylinux

The mpi4py wheels can also be installed (with pip) in conda environments and they should work out of the box, without any special tweak to environment variables, for any of the MPI packages provided by conda-forge_.

Externally-provided MPI implementations may come from a system package manager, sysadmin-maintained builds accessible via module files, or customized user builds. Such usage is supported and encouraged. However, there are a few platform-specific considerations to take into account.

Linux ^^^^^

The Linux (x86_64/aarch64) wheels require one of

• MPICH_ or any other ABI-compatible derivative, like MVAPICH, Intel MPI, HPE Cray MPICH_

• Open MPI_ or any other ABI-compatible derivative, like NVIDIA HPC-X_

Users may need to set the LD_LIBRARY_PATH environment variable such that the dynamic linker is able to find at runtime the MPI shared library file (libmpi.so.*).

Fedora/RHEL ~~~~~~~~~~~

On Fedora/RHEL systems, both MPICH and Open MPI are available for installation. There is no default or preferred MPI implementation. Instead, users must select their favorite MPI implementation by loading the proper MPI module.

.. code:: sh

module load mpi/mpich-$(arch) # for MPICH module load mpi/openmpi-$(arch) # for Open MPI

After loading the requested MPI module, the LD_LIBRARY_PATH environment variable should be properly setup.

Debian/Ubuntu ~~~~~~~~~~~~~

On Debian/Ubuntu systems, Open MPI is the default MPI implementation and most of the MPI-based applications and libraries provided by the distribution depend on Open MPI. Nonetheless, MPICH is also available to users for installation.

In Ubuntu 22.04 and older, due to legacy reasons, the MPICH ABI is slightly broken: the MPI shared library file is named libmpich.so.12 instead of libmpi.so.12 as required by the MPICH ABI Compatibility Initiative <https://www.mpich.org/abi/>_.

Users without sudo access can workaround this issue creating a symbolic link anywhere in their home directory and appending to LD_LIBRARY_PATH.

.. code:: sh

mkdir -p ~/.local/lib libdir=/usr/lib/$(arch)-linux-gnu ln -s $libdir/libmpich.so.12 ~/.local/lib/libmpi.so.12 export LDLIBRARYPATH=$LDLIBRARYPATH:~/.local/lib

A system-wide fix for all users requires sudo access:

.. code:: sh

libdir=/usr/lib/$(arch)-linux-gnu sudo ln -sr $libdir/libmpi{ch,}.so.12

HPE Cray OS ~~~~~~~~~~~

On HPE Cray systems, users must load the cray-mpich-abi module. For further details, refer to man intro_mpi <cray-mpt-mpichabi_>_.

.. cray-mpt-mpichabi: https://cpe.ext.hpe.com/docs/latest/mpt/mpich/intrompi.html#using-mpich-abi-compatibility

macOS ^^^^^

The macOS (arm64/x86_64) wheels require

• MPICH_ or Open MPI_ installed (either manually or via a package manager) in the standard system prefix /usr/local

• MPICH_ or Open MPI_ installed via Homebrew_ in the default prefix /opt/homebrew

• MPICH_ or Open MPI_ installed via MacPorts_ in the default prefix /opt/local

.. _Homebrew: https://brew.sh/ .. _MacPorts: https://www.macports.org/

Windows ^^^^^^^

The Windows (AMD64) wheels require one of

• Intel MPI_

• Microsoft MPI_

User may need to set the I_MPI_ROOT or MSMPI_BIN environment variables such that the MPI dynamic link library (DLL) (impi.dll or msmpi.dll) can be found at runtime.

Intel MPI is under active development and supports recent versions of the MPI standard. Intel MPI can be installed with pip (see the impi-rt_ package on PyPI), being therefore straightforward to get it up and running within a Python environment. Intel MPI can also be installed system-wide as part of the Intel oneAPI HPC Toolkit for Windows or via standalone online/offline installers.

.. _impi-rt: https://pypi.org/project/impi-rt/

Conda packages

The conda-forge_ community provides ready-to-use binary packages from an ever growing collection of software libraries built around the multi-platform conda package manager. Four MPI implementations are available on conda-forge: Open MPI (Linux and macOS), MPICH (Linux and macOS), Intel MPI (Linux and Windows), and Microsoft MPI (Windows). You can install mpi4py and your preferred MPI implementation using the conda_ package manager:

• to use MPICH do:

  .. code:: sh

  conda install -c conda-forge mpi4py mpich

• to use Open MPI do:

  .. code:: sh

  conda install -c conda-forge mpi4py openmpi

• to use Intel MPI do:

  .. code:: sh

  conda install -c conda-forge mpi4py impi_rt

• to use Microsoft MPI do:

  .. code:: sh

  conda install -c conda-forge mpi4py msmpi

MPICH and many of its derivatives are ABI-compatible. You can provide the package specification mpich=X.Y.*=external_* (where X and Y are the major and minor version numbers) to request the conda package manager to use system-provided MPICH (or derivative) libraries. Similarly, you can provide the package specification openmpi=X.Y.*=external_* to use system-provided Open MPI libraries.

The openmpi package on conda-forge has built-in CUDA support, but it is disabled by default. To enable it, follow the instruction outlined during conda install. Additionally, UCX support is also available once the ucx package is installed.

.. warning::

The MPI conda-forge packages are built with special focus on compatibility. The MPICH and Open MPI packages are built in a constrained environment with relatively dated OS images. Therefore, they may lack support for high-performance features like cross-memory attach (XPMEM/CMA). In production scenarios, it is recommended to use external (either custom-built or system-provided) MPI installations. See the relevant conda-forge documentation about using external MPI libraries <cf-mpi-docs_>_ .

.. _conda: https://docs.conda.io .. _conda-forge: https://conda-forge.org/ .. _cf-mpi-docs: https://conda-forge.org/docs/user/tipsandtricks/#using-external-message-passing-interface-mpi-libraries

System packages

mpi4py is readily available through system package managers of most Linux distributions and the most popular community package managers for macOS.

.. _sys-pkg-linux:

Linux ^^^^^

On Fedora Linux systems (as well as RHEL and their derivatives using the EPEL software repository), you can install binary packages with the system package manager:

• using dnf and the mpich package:

  .. code:: sh

  sudo dnf install python3-mpi4py-mpich

• using dnf and the openmpi package:

  .. code:: sh

  sudo dnf install python3-mpi4py-openmpi

Please remember to load the correct MPI module for your chosen MPI implementation:

• for the mpich package do:

  .. code:: sh

  module load mpi/mpich-$(arch) python -c "from mpi4py import MPI"

• for the openmpi package do:

  .. code:: sh

  module load mpi/openmpi-$(arch) python -c "from mpi4py import MPI"

On Ubuntu Linux and Debian Linux systems, binary packages are available for installation using the system package manager:

.. code:: sh

sudo apt install python3-mpi4py

On Arch Linux systems, binary packages are available for installation using the system package manager:

.. code:: sh

sudo pacman -S python-mpi4py

.. _sys-pkg-macos:

macOS ^^^^^

macOS users can install mpi4py using the Homebrew_ package manager:

.. code:: sh

brew install mpi4py

Note that the Homebrew mpi4py package uses Open MPI. Alternatively, install the mpich package and next install mpi4py from sources using pip.

Alternatively, mpi4py can be installed from MacPorts_:

.. code:: sh

sudo port install py-mpi4py

Building from sources

Installing mpi4py from pre-built binary wheels, conda packages, or system packages is not always desired or appropriate. For example, the mpi4py wheels published on PyPI may not be interoperable with non-mainstream, vendor-specific MPI implementations; or a system mpi4py package may be built with a alternative, non-default MPI implementation. In such scenarios, mpi4py can still be installed from its source distribution (sdist) using pip:

.. code:: sh

python -m pip install --no-binary=mpi4py mpi4py

You can also install the in-development version with:

.. code:: sh

python -m pip install git+https://github.com/mpi4py/mpi4py

or:

.. code:: sh

python -m pip install https://github.com/mpi4py/mpi4py/tarball/master

.. note::

Installing mpi4py from its source distribution (available on PyPI) or Git source code repository (available on GitHub) requires a C compiler and a working MPI implementation with development headers and libraries.

.. warning::

pip keeps previously built wheel files in its cache for future reuse. If you want to reinstall the mpi4py package from its source distribution using a different or updated MPI implementation, you have to either first remove the cached wheel file:

.. code:: sh

  python -m pip cache remove mpi4py
  python -m pip install --no-binary=mpi4py mpi4py

or ask pip to disable the cache:

.. code:: sh

  python -m pip install --no-cache-dir --no-binary=mpi4py mpi4py

Citation

If MPI for Python been significant to a project that leads to an academic publication, please acknowledge that fact by citing the project.

• M. Rogowski, S. Aseeri, D. Keyes, and L. Dalcin, mpi4py.futures: MPI-Based Asynchronous Task Execution for Python, IEEE Transactions on Parallel and Distributed Systems, 34(2):611-622, 2023. https://doi.org/10.1109/TPDS.2022.3225481

• L. Dalcin and Y.-L. L. Fang, mpi4py: Status Update After 12 Years of Development, Computing in Science & Engineering, 23(4):47-54, 2021. https://doi.org/10.1109/MCSE.2021.3083216

• L. Dalcin, P. Kler, R. Paz, and A. Cosimo, Parallel Distributed Computing using Python, Advances in Water Resources, 34(9):1124-1139, 2011. https://doi.org/10.1016/j.advwatres.2011.04.013

• L. Dalcin, R. Paz, M. Storti, and J. D'Elia, MPI for Python: performance improvements and MPI-2 extensions, Journal of Parallel and Distributed Computing, 68(5):655-662, 2008. https://doi.org/10.1016/j.jpdc.2007.09.005

• L. Dalcin, R. Paz, and M. Storti, MPI for Python, Journal of Parallel and Distributed Computing, 65(9):1108-1115, 2005. https://doi.org/10.1016/j.jpdc.2005.03.010