Bug#944769: python3-h5py fails to import if offline due to apparent MPI failure

[Drew Parsons]

Source: h5py
Followup-For: Bug #944769

It might not be so simple.  Some of the code is cython, so the obvious
runtime tests don't work, not via os.getenv at least.

For instance, the instance of "if MPI:" in api_types_ext.pxd can be
patched to

  from os import getenv as os_getenv
  OPENMPI_MULTIPROC = os_getenv('OMPI_COMM_WORLD_SIZE') and int(os_getenv('OMPI_COMM_WORLD_SIZE')) > 1
  MPICH_MULTIPROC = os_getenv('MPI_LOCALNRANKS') and int(os_getenv('MPI_LOCALNRANKS'))>1
  MPI_ACTIVE = MPI and ( OPENMPI_MULTIPROC or MPICH_MULTIPROC )
  
  IF MPI_ACTIVE:
      from mpi4py.MPI cimport MPI_Comm, MPI_Info, Comm, Info



But then during configuration cython fails:

  Error compiling Cython file:
  ------------------------------------------------------------
  ...
  from os import getenv as os_getenv
  OPENMPI_MULTIPROC = os_getenv('OMPI_COMM_WORLD_SIZE') and int(os_getenv('OMPI_COMM_WORLD_SIZE')) > 1
  MPICH_MULTIPROC = os_getenv('MPI_LOCALNRANKS') and int(os_getenv('MPI_LOCALNRANKS'))>1
  MPI_ACTIVE = MPI and ( OPENMPI_MULTIPROC or MPICH_MULTIPROC )
  
  IF MPI_ACTIVE:
    ^
  ------------------------------------------------------------
  
  h5py/api_types_ext.pxd:22:3: Compile-time name 'MPI_ACTIVE' not defined


even though MPI_ACTIVE is defined in code right there.

I haven't coded in cython before, perhaps it needs a different syntax?