Compatibility with mpi4py <= 1.3.1.

.gitignore

@@ -14,3 +14,4 @@
 /sharp_oracle.inc
 
 /python/libsharp/libsharp.c
+/python/libsharp/libsharp_mpi.c

python/libsharp/libsharp.pyx

@@ -105,7 +105,8 @@ def sht(jobtype, geom_info ginfo, alm_info ainfo, double[:, :, ::1] input,
         from mpi4py import MPI
         if not isinstance(comm, MPI.Comm):
             raise TypeError('comm must be an mpi4py communicator')
-        comm_ptr = <void*><size_t>MPI._addressof(comm)
+        from .libsharp_mpi import _addressof
+        comm_ptr = <void*><size_t>_addressof(comm)
         with nogil:
             r = sharp_execute_mpi_maybe (
                 comm_ptr, jobtype_i,

python/libsharp/libsharp_mpi.pyx

@@ -0,0 +1,10 @@
+from mpi4py.MPI cimport Comm
+cdef extern from "Python.h":
+    object PyLong_FromVoidPtr(void*)
+
+# For compatibility with mpi4py <= 1.3.1
+# Newer versions could use the MPI._addressof function
+def _addressof(comm):
+    cdef void *ptr = NULL
+    ptr = <void*>&(<Comm>comm).ob_mpi
+    return PyLong_FromVoidPtr(ptr)