CHANGES

Release 4.1.1 [2025-10-10]

• Add MPIABI-aware import hook support.

• Support MPI.ERR_ERRHANDLER with Open MPI.

• Fix Windows build issues with Intel MPI 2021.16.

• Minor fixes and improvements to typing stubs.

• Minor fixes to documentation.

• Publish Python 3.8-3.14 and PyPy 3.11 wheels.

• PyPy 3.10 (EOL) wheels are no longer published.

Release 4.1.0 [2025-06-25]

• New features:

  • Publish binary wheel packages on PyPI with support for multiple operating systems (Linux, macOS, Windows), processor architectures (AMD64, ARM64), MPI implementations (MPICH, Open MPI, and their ABI-compatible derivatives), and Python implementations (CPython, PyPy).

  • Add support for the MPI 5.0 standard.

    • MPI handle serialization with integral values.

    • Fixed-size Fortran LOGICAL datatypes.

    • Query ABI version/info and Fortran ABI info.

  • MPI.Datatype.Create_contiguous now uses BigMPI’s approach when using MPI implementations that do not yet support the MPI 4.0 large-count APIs.

  • Add support for MPI.FLOAT16_T and MPI.BFLOAT16_T datatypes. These datatypes are not yet standard but available as extensions in MPI implementations.

  • Add MPI.Status.tomemory to expose the status contents as a memoryview object.

• Enhancements:

  • Support (opt-in via MPI4PY_BUILD_PYSABI) for building with Py_LIMITED_API under Python 3.10+ (requires Cython 3.1+).

  • Support (opt-in via MPI4PY_BUILD_MPIABI) for building with the MPI 5.0 standard ABI and the MPICH or Open MPI legacy ABIs. The MPI extension module will be able to dynamically link at runtime with older versions (down to the MPI 3.0 standard) of the MPI implementation used at compile time. Only available on Linux, macOS, and Windows.

  • Support a buffersize parameter in the MPIPoolExecutor.map() and MPIPoolExecutor.starmap() methods to limit the number of pending tasks.

  • Improve ownership management of DLPack capsules.

  • Reimplement MPI DLL search path on Windows.

  • Minor fixes to typing stubs and documentation.

• Backward-incompatible changes:

  • Python 3.8+ is required.

  • The MPI.Exception class is now a heap type.

  • The types of the MPI.BOTTOM, MPI.IN_PLACE, and MPI.BUFFER_AUTOMATIC are no longer subclasses of int.

Release 4.0.3 [2025-02-13]

• Fix DLPack v1.0 support.

Release 4.0.2 [2025-02-01]

• Support MPI-4 features within Intel MPI 2021.14.

• Various fixes and updates to tests.

• Minor fixes to typing support.

• Minor fix to documentation.

Release 4.0.1 [2024-10-11]

• Update support for Python 3.13:

  • Enable Cython 3.1 support for free-threaded CPython.

  • Allow compiling Cython-generated C sources with the full Python C-API.

  • Fix MPI DLL path workarounds on Windows after changes to locals().

• Enhancements to test suite:

  • Support XML reports via unittest-xml-reporting.

  • Add command line options to exclude tests by patterns and files.

  • Refactor Python 2 code to use Python 3 constructs using pyupgrade.

• Miscellaneous:

  • Minor and mostly inconsequential subclass fix in mpi4py.util.pkl5.

  • Update compatibility workarounds for legacy MPICH 3.0 release.

Release 4.0.0 [2024-07-28]

• New features:

  • Add support for the MPI-4.0 standard.

    • Use large count MPI-4 routines.

    • Add persistent collective communication.

    • Add partitioned point-to-point communication.

    • Add new communicator constructors.

    • Add the Session class and its methods.

  • Add support for the MPI-4.1 standard.

    • Add non-destructive completion test for multiple requests.

    • Add value-index datatype constructor.

    • Add communicator/session buffer attach/detach/flush.

    • Support for removal of error classes/codes/strings.

    • Support for querying hardware resource information.

  • Add preliminary support for the upcoming MPI-5.0 standard.

    • User-level failure mitigation (ULFM).

  • mpi4py.util.pool: New drop-in replacement for multiprocessing.pool.

  • mpi4py.util.sync: New synchronization utilities.

  • Add runtime check for mismatch between mpiexec and MPI library.

  • Support scikit-build-core as an alternative build backend.

  • Support meson-python as an alternative build backend.

• Enhancements:

  • mpi4py.futures: Support for parallel tasks.

  • mpi4py.futures: Report exception tracebacks in workers.

  • mpi4py.util.pkl5: Add support for collective communication.

  • Add methods Datatype.fromcode(), Datatype.tocode() and attributes Datatype.typestr, Datatype.typechar to simplify NumPy interoperability for simple cases.

  • Add methods Comm.Create_errhandler(), Win.Create_errhandler(), and File.Create_errhandler() to create custom error handlers.

  • Add support for pickle serialization of instances of MPI types. All instances of Datatype, Info, and Status can be serialized. Instances of Op can be serialized only if created through mpi4py by calling Op.Create(). Instances of other MPI types can be serialized only if they reference predefined handles.

  • Add handle attribute and fromhandle() class method to MPI classes to ease interoperability with external code. The handle value is an unsigned integer guaranteed to fit on the platform’s uintptr_t C type.

  • Add lowercase free() method to MPI classes to ease MPI object deallocation and cleanup. This method eventually attempts to call Free(), but only if the object’s MPI handle is not a null or predefined handle, and such call is allowed within the World Model init/finalize.

• Backward-incompatible changes:

  • Python 2 is no longer supported, Python 3.6+ is required, but typing stubs are supported for Python 3.8+.

  • The Intracomm.Create_group() method is no longer defined in the base Comm class.

  • Group.Compare() and Comm.Compare() are no longer class methods but instance methods. Existing codes using the former class methods are expected to continue working.

  • Group.Translate_ranks() is no longer a class method but an instance method. Existing codes using the former class method are expected to continue working.

  • The LB and UB datatypes are no longer available, use Datatype.Create_resized() instead.

  • The HOST predefined attribute key is no longer available.

  • The MPI.memory class has been renamed to MPI.buffer. The old name is still available as an alias to the new name.

  • The mpi4py.dl module is no longer available.

  • The mpi4py.get_config function returns an empty dictionary.

• Miscellaneous:

  • The project is now licensed under the BSD-3-Clause license. This change is fairly inconsequential for users and distributors. It simply adds an additional clause against using contributor names for promotional purposes without their consent.

  • Add a new guidelines section to documentation laying out new fair play rules. These rules ask companies and outside developers to refrain from reusing the mpi4py name in unaffiliated projects, publishing binary mpi4py wheels on the main Python Package Index (PyPI), and distributing modified versions with incompatible or extended API changes. The primary motivation of these rules is to avoid fragmentation and end-user confusion.

Release 3.1.6 [2024-04-14]

Warning

This is the last release supporting Python 2.

• Fix various build issues.

Release 3.1.5 [2023-10-04]

Warning

This is the last release supporting Python 2.

• Rebuild C sources with Cython 0.29.36 to support Python 3.12.

Release 3.1.4 [2022-11-02]

Warning

This is the last release supporting Python 2.

• Rebuild C sources with Cython 0.29.32 to support Python 3.11.

• Fix contiguity check for DLPack and CAI buffers.

• Workaround build failures with setuptools v60.

Release 3.1.3 [2021-11-25]

Warning

This is the last release supporting Python 2.

• Add missing support for MPI.BOTTOM to generalized all-to-all collectives.

Release 3.1.2 [2021-11-04]

Warning

This is the last release supporting Python 2.

• mpi4py.futures: Add _max_workers property to MPIPoolExecutor.

• mpi4py.util.dtlib: Fix computation of alignment for predefined datatypes.

• mpi4py.util.pkl5: Fix deadlock when using ssend() + mprobe().

• mpi4py.util.pkl5: Add environment variable MPI4PY_PICKLE_THRESHOLD.

• mpi4py.rc: Interpret "y" and "n" strings as boolean values.

• Fix/add typemap/typestr for MPI.WCHAR/MPI.COUNT datatypes.

• Minor fixes and additions to documentation.

• Minor fixes to typing support.

• Support for local version identifier (PEP-440).

Release 3.1.1 [2021-08-14]

Warning

This is the last release supporting Python 2.

• Fix typo in Requires-Python package metadata.

• Regenerate C sources with Cython 0.29.24.

Release 3.1.0 [2021-08-12]

Warning

This is the last release supporting Python 2.

• New features:

  • mpi4py.util: New package collecting miscellaneous utilities.

• Enhancements:

  • Add pickle-based Request.waitsome() and Request.testsome().

  • Add lowercase methods Request.get_status() and Request.cancel().

  • Support for passing Python GPU arrays compliant with the DLPack data interchange mechanism (link) and the __cuda_array_interface__ (CAI) standard (link) to uppercase methods. This support requires that mpi4py is built against CUDA-aware MPI implementations. This feature is currently experimental and subject to future changes.

  • mpi4py.futures: Add support for initializers and canceling futures at shutdown. Environment variables names now follow the pattern MPI4PY_FUTURES_*, the previous MPI4PY_* names are deprecated.

  • Add type annotations to Cython code. The first line of the docstring of functions and methods displays a signature including type annotations.

  • Add companion stub files to support type checkers.

  • Support for weak references.

• Miscellaneous:

  • Add a new mpi4py publication (link) to the citation listing.

Release 3.0.3 [2019-11-04]

• Regenerate Cython wrappers to support Python 3.8.

Release 3.0.2 [2019-06-11]

• Bug fixes:

  • Fix handling of readonly buffers in support for Python 2 legacy buffer interface. The issue triggers only when using a buffer-like object that is readonly and does not export the new Python 3 buffer interface.

  • Fix build issues with Open MPI 4.0.x series related to removal of many MPI-1 symbols deprecated in MPI-2 and removed in MPI-3.

  • Minor documentation fixes.

Release 3.0.1 [2019-02-15]

• Bug fixes:

  • Fix Comm.scatter() and other collectives corrupting input send list. Add safety measures to prevent related issues in global reduction operations.

  • Fix error-checking code for counts in Op.Reduce_local().

• Enhancements:

  • Map size-specific Python/NumPy typecodes to MPI datatypes.

  • Allow partial specification of target list/tuple arguments in the various Win RMA methods.

  • Workaround for removal of MPI_{LB|UB} in Open MPI 4.0.

  • Support for Microsoft MPI v10.0.

Release 3.0.0 [2017-11-08]

• New features:

  • mpi4py.futures: Execute computations asynchronously using a pool of MPI processes. This package is based on concurrent.futures from the Python standard library.

  • mpi4py.run: Run Python code and abort execution in case of unhandled exceptions to prevent deadlocks.

  • mpi4py.bench: Run basic MPI benchmarks and tests.

• Enhancements:

  • Lowercase, pickle-based collective communication calls are now thread-safe through the use of fine-grained locking.

  • The MPI module now exposes a memory type which is a lightweight variant of the builtin memoryview type, but exposes both the legacy Python 2 and the modern Python 3 buffer interface under a Python 2 runtime.

  • The MPI.Comm.Alltoallw() method now uses count=1 and displ=0 as defaults, assuming that messages are specified through user-defined datatypes.

  • The Request.Wait[all]() methods now return True to match the interface of Request.Test[all]().

  • The Win class now implements the Python buffer interface.

• Backward-incompatible changes:

  • The buf argument of the MPI.Comm.recv() method is deprecated, passing anything but None emits a warning.

  • The MPI.Win.memory property was removed, use the MPI.Win.tomemory() method instead.

  • Executing python -m mpi4py in the command line is now equivalent to python -m mpi4py.run. For the former behavior, use python -m mpi4py.bench.

  • Python 2.6 and 3.2 are no longer supported. The mpi4py.MPI module may still build and partially work, but other pure-Python modules under the mpi4py namespace will not.

  • Windows: Remove support for legacy MPICH2, Open MPI, and DeinoMPI.

Release 2.0.0 [2015-10-18]

• Support for MPI-3 features.

  • Matched probes and receives.

  • Nonblocking collectives.

  • Neighborhood collectives.

  • New communicator constructors.

  • Request-based RMA operations.

  • New RMA communication and synchronisation calls.

  • New window constructors.

  • New datatype constructor.

  • New C++ boolean and floating complex datatypes.

• Support for MPI-2 features not included in previous releases.

  • Generalized All-to-All collective (Comm.Alltoallw())

  • User-defined data representations (Register_datarep())

• New scalable implementation of reduction operations for Python objects. This code is based on binomial tree algorithms using point-to-point communication and duplicated communicator contexts. To disable this feature, use mpi4py.rc.fast_reduce = False.

• Backward-incompatible changes:

  • Python 2.4, 2.5, 3.0 and 3.1 are no longer supported.

  • Default MPI error handling policies are overridden. After import, mpi4py sets the ERRORS_RETURN error handler in COMM_SELF and COMM_WORLD, as well as any new Comm, Win, or File instance created through mpi4py, thus effectively ignoring the MPI rules about error handler inheritance. This way, MPI errors translate to Python exceptions. To disable this behavior and use the standard MPI error handling rules, use mpi4py.rc.errors = 'default'.

  • Change signature of all send methods, dest is a required argument.

  • Change signature of all receive and probe methods, source defaults to ANY_SOURCE, tag defaults to ANY_TAG.

  • Change signature of send lowercase-spelling methods, obj arguments are not mandatory.

  • Change signature of recv lowercase-spelling methods, renamed ‘obj’ arguments to ‘buf’.

  • Change Request.Waitsome() and Request.Testsome() to return None or list.

  • Change signature of all lowercase-spelling collectives, sendobj arguments are now mandatory, recvobj arguments were removed.

  • Reduction operations MAXLOC and MINLOC are no longer special-cased in lowercase-spelling methods Comm.[all]reduce() and Comm.[ex]scan(), the input object must be specified as a tuple (obj, location).

  • Change signature of name publishing functions. The new signatures are Publish_name(service_name, port_name, info=INFO_NULL) and Unpublish_name(service_name, port_name, info=INFO_NULL)`.

  • Win instances now cache Python objects exposing memory by keeping references instead of using MPI attribute caching.

  • Change signature of Win.Lock(). The new signature is Win.Lock(rank, lock_type=LOCK_EXCLUSIVE, assertion=0).

  • Move Cartcomm.Map() to Intracomm.Cart_map().

  • Move Graphcomm.Map() to Intracomm.Graph_map().

  • Remove the mpi4py.MPE module.

  • Rename the Cython definition file for use with cimport statement from mpi_c.pxd to libmpi.pxd.

Release 1.3.1 [2013-08-07]

• Regenerate C wrappers with Cython 0.19.1 to support Python 3.3.

• Install *.pxd files in <site-packages>/mpi4py to ease the support for Cython’s cimport statement in code requiring to access mpi4py internals.

• As a side-effect of using Cython 0.19.1, ancient Python 2.3 is no longer supported. If you really need it, you can install an older Cython and run python setup.py build_src --force.

Release 1.3 [2012-01-20]

• Now Comm.recv() accept a buffer to receive the message.

• Add Comm.irecv() and Request.{wait|test}[any|all]().

• Add Intracomm.Spawn_multiple().

• Better buffer handling for PEP 3118 and legacy buffer interfaces.

• Add support for attribute attribute caching on communicators, datatypes and windows.

• Install MPI-enabled Python interpreter as <path>/mpi4py/bin/python-mpi.

• Windows: Support for building with Open MPI.

Release 1.2.2 [2010-09-13]

• Add mpi4py.get_config() to retrieve information (compiler wrappers, includes, libraries, etc) about the MPI implementation employed to build mpi4py.

• Workaround Python libraries with missing GILState-related API calls in case of non-threaded Python builds.

• Windows: look for MPICH2, DeinoMPI, Microsoft HPC Pack at their default install locations under %ProgramFiles.

• MPE: fix hacks related to old API’s, these hacks are broken when MPE is built with a MPI implementations other than MPICH2.

• HP-MPI: fix for missing Fortran datatypes, use dlopen() to load the MPI shared library before MPI_Init()

• Many distutils-related fixes, cleanup, and enhancements, better logics to find MPI compiler wrappers.

• Support for pip install mpi4py.

Release 1.2.1 [2010-02-26]

• Fix declaration in Cython include file. This declaration, while valid for Cython, broke the simple-minded parsing used in conf/mpidistutils.py to implement configure-tests for availability of MPI symbols.

• Update SWIG support and make it compatible with Python 3. Also generate an warning for SWIG < 1.3.28.

• Fix distutils-related issues in Mac OS X. Now ARCHFLAGS environment variable is honored of all Python’s config/Makefile variables.

• Fix issues with Open MPI < 1.4.2 related to error checking and MPI_XXX_NULL handles.

Release 1.2 [2009-12-29]

• Automatic MPI datatype discovery for NumPy arrays and PEP-3118 buffers. Now buffer-like objects can be messaged directly, it is no longer required to explicitly pass a 2/3-list/tuple like [data, MPI.DOUBLE], or [data, count, MPI.DOUBLE]. Only basic types are supported, i.e., all C/C99-native signed/unsigned integral types and single/double precision real/complex floating types. Many thanks to Eilif Muller for the initial feedback.

• Nonblocking send of pickled Python objects. Many thanks to Andreas Kloeckner for the initial patch and enlightening discussion about this enhancement.

• Request instances now hold a reference to the Python object exposing the buffer involved in point-to-point communication or parallel I/O. Many thanks to Andreas Kloeckner for the initial feedback.

• Support for logging of user-defined states and events using MPE. Runtime (i.e., without requiring a recompile!) activation of logging of all MPI calls is supported in POSIX platforms implementing dlopen().

• Support for all the new features in MPI-2.2 (new C99 and F90 datatypes, distributed graph topology, local reduction operation, and other minor enhancements).

• Fix the annoying issues related to Open MPI and Python dynamic loading of extension modules in platforms supporting dlopen().

• Fix SLURM dynamic loading issues on SiCortex. Many thanks to Ian Langmore for providing me shell access.

Release 1.1.0 [2009-06-06]

• Fix bug in Comm.Iprobe() that caused segfaults as Python C-API calls were issued with the GIL released (issue #2).

• Add Comm.bsend() and Comm.ssend() for buffered and synchronous send semantics when communicating general Python objects.

• Now the call Info.Get(key) return a single value (i.e, instead of a 2-tuple); this value is None if key is not in the Info object, or a string otherwise. Previously, the call redundantly returned (None, False) for missing key-value pairs; None is enough to signal a missing entry.

• Add support for parametrized Fortran datatypes.

• Add support for decoding user-defined datatypes.

• Add support for user-defined reduction operations on memory buffers. However, at most 16 user-defined reduction operations can be created. Ask the author for more room if you need it.

Release 1.0.0 [2009-03-20]

This is the fist release of the all-new, Cython-based, implementation of MPI for Python. Unfortunately, this implementation is not backward-compatible with the previous one. The list below summarizes the more important changes that can impact user codes.

• Some communication calls had overloaded functionality. Now there is a clear distinction between communication of general Python object with pickle, and (fast, near C-speed) communication of buffer-like objects (e.g., NumPy arrays).

  • for communicating general Python objects, you have to use all-lowercase methods, like send(), recv(), bcast(), etc.

  • for communicating array data, you have to use Send(), Recv(), Bcast(), etc. methods. Buffer arguments to these calls must be explicitly specified by using a 2/3-list/tuple like [data, MPI.DOUBLE], or [data, count, MPI.DOUBLE] (the former one uses the byte-size of data and the extent of the MPI datatype to define the count).

• Indexing a communicator with an integer returned a special object associating the communication with a target rank, alleviating you from specifying source/destination/root arguments in point-to-point and collective communications. This functionality is no longer available, expressions like:

  MPI.COMM_WORLD[0].Send(...)
  MPI.COMM_WORLD[0].Recv(...)
  MPI.COMM_WORLD[0].Bcast(...)
  

  have to be replaced by:

  MPI.COMM_WORLD.Send(..., dest=0)
  MPI.COMM_WORLD.Recv(..., source=0)
  MPI.COMM_WORLD.Bcast(..., root=0)
  

• Automatic MPI initialization (i.e., at import time) requests the maximum level of MPI thread support (i.e., it is done by calling MPI_Init_thread() and passing MPI_THREAD_MULTIPLE). In case you need to change this behavior, you can tweak the contents of the mpi4py.rc module.

• In order to obtain the values of predefined attributes attached to the world communicator, now you have to use the Get_attr() method on the MPI.COMM_WORLD instance:

  tag_ub = MPI.COMM_WORLD.Get_attr(MPI.TAG_UB)
  

• In the previous implementation, MPI.COMM_WORLD and MPI.COMM_SELF were associated to duplicates of the (C-level) MPI_COMM_WORLD and MPI_COMM_SELF predefined communicator handles. Now this is no longer the case, MPI.COMM_WORLD and MPI.COMM_SELF proxies the actual MPI_COMM_WORLD and MPI_COMM_SELF handles.

• Convenience aliases MPI.WORLD and MPI.SELF were removed. Use instead MPI.COMM_WORLD and MPI.COMM_SELF.

• Convenience constants MPI.WORLD_SIZE and MPI.WORLD_RANK were removed. Use instead MPI.COMM_WORLD.Get_size() and MPI.COMM_WORLD.Get_rank().