From bfb9bc07337df950ea2f75bc2c0f6e45cb443c7e Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Thu, 16 Oct 2025 16:23:11 +0200
Subject: [PATCH 01/13] add file ddm/mpi.py for MockMPI and MPIWrapper
 (previously in Struphy, now moved here)

---
 psydac/ddm/cart.py |  21 ++++++---
 psydac/ddm/mpi.py  | 105 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 120 insertions(+), 6 deletions(-)
 create mode 100644 psydac/ddm/mpi.py

diff --git a/psydac/ddm/cart.py b/psydac/ddm/cart.py
index 56251b22c..49714512f 100644
--- a/psydac/ddm/cart.py
+++ b/psydac/ddm/cart.py
@@ -3,8 +3,14 @@
 import os
 import numpy as np
 from itertools import product
-from mpi4py    import MPI
-
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
+    
+from psydac.ddm.mpi import MockMPI
 from psydac.ddm.partition import compute_dims, partition_procs_per_patch
 
 
@@ -31,11 +37,14 @@ def find_mpi_type( dtype ):
         MPI datatype to be used for communication.
 
     """
-    if isinstance( dtype, MPI.Datatype ):
-        mpi_type = dtype
+    if not isinstance(MPI, MockMPI):
+        if isinstance( dtype, MPI.Datatype ):
+            mpi_type = dtype
+        else:
+            nt = np.dtype( dtype )
+            mpi_type = MPI._typedict[nt.char]
     else:
-        nt = np.dtype( dtype )
-        mpi_type = MPI._typedict[nt.char]
+        mpi_type = np.dtype( dtype )
 
     return mpi_type
 
diff --git a/psydac/ddm/mpi.py b/psydac/ddm/mpi.py
new file mode 100644
index 000000000..d4a31a118
--- /dev/null
+++ b/psydac/ddm/mpi.py
@@ -0,0 +1,105 @@
+from dataclasses import dataclass
+from time import time
+from typing import TYPE_CHECKING
+
+
+# Might not be needed
+class MPICommWrapper:
+    def __init__(self, use_mpi=True):
+        self.use_mpi = use_mpi
+        if use_mpi:
+            from mpi4py import MPI
+
+            self.comm = MPI.COMM_WORLD
+        else:
+            self.comm = MockComm()
+
+    def __getattr__(self, name):
+        return getattr(self.comm, name)
+
+
+class MockComm:
+    def __getattr__(self, name):
+        # Return a function that does nothing and returns None
+        def dummy(*args, **kwargs):
+            return None
+
+        return dummy
+
+    # Override some functions
+    def Get_rank(self):
+        return 0
+
+    def Get_size(self):
+        return 1
+
+    def Barrier(self):
+        return
+
+
+class MPIwrapper:
+    def __init__(self, use_mpi: bool = False):
+        self.use_mpi = use_mpi
+        if use_mpi:
+            from mpi4py import MPI
+
+            self._MPI = MPI
+            print("MPI is enabled")
+        else:
+            self._MPI = MockMPI()
+            print("MPI is NOT enabled")
+
+    @property
+    def MPI(self):
+        return self._MPI
+
+
+class MockMPI:
+    def __getattr__(self, name):
+        # Return a function that does nothing and returns None
+        def dummy(*args, **kwargs):
+            return None
+
+        return dummy
+
+    # Override some functions
+    @property
+    def COMM_WORLD(self):
+        return MockComm()
+    
+    class Comm:
+        x = None
+
+    # def comm_Get_rank(self):
+    #     return 0
+
+    # def comm_Get_size(self):
+    #     return 1
+
+
+try:
+    from mpi4py import MPI
+
+    _comm = MPI.COMM_WORLD
+    rank = _comm.Get_rank()
+    size = _comm.Get_size()
+    mpi_enabled = size > 1
+except ImportError:
+    # mpi4py not installed
+    mpi_enabled = False
+except Exception:
+    # mpi4py installed but not running under mpirun
+    mpi_enabled = False
+
+# TODO: add environment variable for mpi use
+mpi_wrapper = MPIwrapper(use_mpi=mpi_enabled)
+
+# TYPE_CHECKING is True when type checking (e.g., mypy), but False at runtime.
+if TYPE_CHECKING:
+    from mpi4py import MPI
+
+    mpi = MPI
+else:
+    mpi = mpi_wrapper.MPI
+
+print(f"{mpi = }")
\ No newline at end of file

From 2f39539206272427e7a5b3e15df12bf60a235f67 Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Thu, 16 Oct 2025 16:58:20 +0200
Subject: [PATCH 02/13] fix assertions in cart.py

---
 psydac/ddm/cart.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/psydac/ddm/cart.py b/psydac/ddm/cart.py
index 49714512f..78a2bf78b 100644
--- a/psydac/ddm/cart.py
+++ b/psydac/ddm/cart.py
@@ -72,7 +72,8 @@ class MultiPatchDomainDecomposition:
     def __init__(self, ncells, periods, comm=None, num_threads=None):
 
         assert len( ncells ) == len( periods )
-        if comm is not None:assert isinstance( comm, MPI.Comm )
+        if not isinstance(MPI, MockMPI) and comm is not None:
+            assert isinstance( comm, MPI.Comm )
         num_threads = num_threads if num_threads else int(os.environ.get('OMP_NUM_THREADS', 1))
 
         # Store input arguments
@@ -215,7 +216,8 @@ def __init__(self, ncells, periods, comm=None, global_comm=None, num_threads=Non
         assert len( ncells ) == len( periods )
         assert all( n >=1 for n in ncells )
         assert all( isinstance( period, bool ) for period in periods )
-        if comm is not None: assert isinstance( comm, MPI.Comm )
+        if not isinstance(MPI, MockMPI) and comm is not None:
+            assert isinstance( comm, MPI.Comm )
 
         self._ncells       = tuple ( ncells )
         self._periods      = tuple ( periods )

From 73ece1cf90efaf61015c1d30f61aa32c8615ac4a Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Thu, 16 Oct 2025 17:20:43 +0200
Subject: [PATCH 03/13] fix mpi4py imports everywhere

---
 mpi_tester.py                                 | 16 +++++++++++++--
 psydac/ddm/blocking_data_exchanger.py         |  7 ++++++-
 psydac/ddm/cart.py                            |  8 ++++++--
 psydac/ddm/interface_data_exchanger.py        |  7 ++++++-
 psydac/ddm/nonblocking_data_exchanger.py      |  7 ++++++-
 psydac/ddm/tests/test_cart_1d.py              |  8 +++++++-
 psydac/ddm/tests/test_cart_2d.py              |  8 +++++++-
 psydac/ddm/tests/test_cart_3d.py              |  8 +++++++-
 psydac/ddm/tests/test_multicart_2d.py         |  8 +++++++-
 psydac/fem/partitioning.py                    |  7 ++++++-
 psydac/fem/tensor.py                          |  8 +++++++-
 psydac/fem/tests/test_spline_interpolation.py |  8 +++++++-
 psydac/fem/tests/test_splines_par.py          |  7 ++++++-
 psydac/linalg/block.py                        |  8 +++++++-
 psydac/linalg/stencil.py                      |  7 ++++++-
 psydac/linalg/tests/test_block.py             | 16 +++++++--------
 psydac/linalg/tests/test_fft.py               |  7 ++++++-
 .../tests/test_stencil_interface_matrix.py    |  8 +++++++-
 psydac/linalg/tests/test_stencil_vector.py    | 20 +++++++++----------
 .../linalg/tests/test_stencil_vector_space.py | 14 ++++++-------
 20 files changed, 140 insertions(+), 47 deletions(-)

diff --git a/mpi_tester.py b/mpi_tester.py
index ca3dba1ae..c6eb32a8f 100644
--- a/mpi_tester.py
+++ b/mpi_tester.py
@@ -101,7 +101,13 @@ def MPITest(commsize):
     def test_stuff(comm):
         pass
     """
-    from mpi4py import MPI
+    from typing import TYPE_CHECKING
+
+    if TYPE_CHECKING:
+        from mpi4py import MPI
+    else:
+        from psydac.ddm.mpi import mpi as MPI
+        
     if not isinstance(commsize, (tuple, list)):
         commsize = (commsize,)
 
@@ -182,7 +188,13 @@ def __init__(self):
     #---------------------------------------------------------------------------
     @property
     def comm(self):
-        from mpi4py import MPI
+        from typing import TYPE_CHECKING
+
+        if TYPE_CHECKING:
+            from mpi4py import MPI
+        else:
+            from psydac.ddm.mpi import mpi as MPI
+            
         return MPI.COMM_WORLD
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/blocking_data_exchanger.py b/psydac/ddm/blocking_data_exchanger.py
index ca83b140a..df9df0c3e 100644
--- a/psydac/ddm/blocking_data_exchanger.py
+++ b/psydac/ddm/blocking_data_exchanger.py
@@ -1,7 +1,12 @@
 # coding: utf-8
 
 import numpy as np
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from .cart import CartDecomposition, find_mpi_type
 from .basic import CartDataExchanger
diff --git a/psydac/ddm/cart.py b/psydac/ddm/cart.py
index 78a2bf78b..b4c00de01 100644
--- a/psydac/ddm/cart.py
+++ b/psydac/ddm/cart.py
@@ -216,8 +216,12 @@ def __init__(self, ncells, periods, comm=None, global_comm=None, num_threads=Non
         assert len( ncells ) == len( periods )
         assert all( n >=1 for n in ncells )
         assert all( isinstance( period, bool ) for period in periods )
-        if not isinstance(MPI, MockMPI) and comm is not None:
-            assert isinstance( comm, MPI.Comm )
+        if isinstance(MPI, MockMPI): 
+            comm = None
+        else:
+            if comm is not None:
+                assert isinstance( comm, MPI.Comm )
+        
 
         self._ncells       = tuple ( ncells )
         self._periods      = tuple ( periods )
diff --git a/psydac/ddm/interface_data_exchanger.py b/psydac/ddm/interface_data_exchanger.py
index cd60d8792..fb74ab4f7 100644
--- a/psydac/ddm/interface_data_exchanger.py
+++ b/psydac/ddm/interface_data_exchanger.py
@@ -1,6 +1,11 @@
 # coding: utf-8
 
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from .cart import InterfaceCartDecomposition, find_mpi_type
 
diff --git a/psydac/ddm/nonblocking_data_exchanger.py b/psydac/ddm/nonblocking_data_exchanger.py
index 4c482518d..88a6ae334 100644
--- a/psydac/ddm/nonblocking_data_exchanger.py
+++ b/psydac/ddm/nonblocking_data_exchanger.py
@@ -2,7 +2,12 @@
 
 import numpy as np
 from itertools import product
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from .cart import CartDecomposition, find_mpi_type
 from .basic import CartDataExchanger
diff --git a/psydac/ddm/tests/test_cart_1d.py b/psydac/ddm/tests/test_cart_1d.py
index b3e51d3ad..55d7b7011 100644
--- a/psydac/ddm/tests/test_cart_1d.py
+++ b/psydac/ddm/tests/test_cart_1d.py
@@ -11,7 +11,13 @@
 def run_cart_1d( data_exchanger_type, verbose=False ):
 
     import numpy as np
-    from mpi4py       import MPI
+    from typing import TYPE_CHECKING
+
+    if TYPE_CHECKING:
+        from mpi4py import MPI
+    else:
+        from psydac.ddm.mpi import mpi as MPI
+        
     from psydac.ddm.cart import DomainDecomposition, CartDecomposition
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/tests/test_cart_2d.py b/psydac/ddm/tests/test_cart_2d.py
index 5974a50a9..f2c24260b 100644
--- a/psydac/ddm/tests/test_cart_2d.py
+++ b/psydac/ddm/tests/test_cart_2d.py
@@ -9,7 +9,13 @@
 def run_cart_2d( data_exchanger_type, verbose=False , nprocs=None, reverse_axis=None):
 
     import numpy as np
-    from mpi4py       import MPI
+    from typing import TYPE_CHECKING
+
+    if TYPE_CHECKING:
+        from mpi4py import MPI
+    else:
+        from psydac.ddm.mpi import mpi as MPI
+        
     from psydac.ddm.cart import DomainDecomposition, CartDecomposition
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/tests/test_cart_3d.py b/psydac/ddm/tests/test_cart_3d.py
index 20b6326f4..00ba32b88 100644
--- a/psydac/ddm/tests/test_cart_3d.py
+++ b/psydac/ddm/tests/test_cart_3d.py
@@ -9,7 +9,13 @@
 def run_cart_3d( data_exchanger_type, verbose=False ):
 
     import numpy as np
-    from mpi4py       import MPI
+    from typing import TYPE_CHECKING
+
+    if TYPE_CHECKING:
+        from mpi4py import MPI
+    else:
+        from psydac.ddm.mpi import mpi as MPI
+        
     from psydac.ddm.cart import DomainDecomposition, CartDecomposition
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/tests/test_multicart_2d.py b/psydac/ddm/tests/test_multicart_2d.py
index 4b1bbddb3..062749430 100644
--- a/psydac/ddm/tests/test_multicart_2d.py
+++ b/psydac/ddm/tests/test_multicart_2d.py
@@ -36,7 +36,13 @@ def get_plus_starts_ends(minus_starts, minus_ends, minus_npts, plus_npts, minus_
 #===============================================================================
 def run_carts_2d():
     import numpy as np
-    from mpi4py          import MPI
+    from typing import TYPE_CHECKING
+
+    if TYPE_CHECKING:
+        from mpi4py import MPI
+    else:
+        from psydac.ddm.mpi import mpi as MPI
+        
     from psydac.ddm.cart import MultiPatchDomainDecomposition, CartDecomposition, create_interfaces_cart
     from psydac.ddm.blocking_data_exchanger  import BlockingCartDataExchanger
     from psydac.ddm.interface_data_exchanger import InterfaceCartDataExchanger
diff --git a/psydac/fem/partitioning.py b/psydac/fem/partitioning.py
index 33b3e90a3..804cf87e2 100644
--- a/psydac/fem/partitioning.py
+++ b/psydac/fem/partitioning.py
@@ -2,7 +2,12 @@
 import os
 
 import numpy as np
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.ddm.cart       import CartDecomposition, InterfaceCartDecomposition, create_interfaces_cart
 from psydac.core.bsplines  import elements_spans
diff --git a/psydac/fem/tensor.py b/psydac/fem/tensor.py
index 39736af1f..02203922c 100644
--- a/psydac/fem/tensor.py
+++ b/psydac/fem/tensor.py
@@ -5,7 +5,13 @@
 of compact support
 
 """
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
+    
 import numpy as np
 import itertools
 import h5py
diff --git a/psydac/fem/tests/test_spline_interpolation.py b/psydac/fem/tests/test_spline_interpolation.py
index 6e27d60ca..b2777a46b 100644
--- a/psydac/fem/tests/test_spline_interpolation.py
+++ b/psydac/fem/tests/test_spline_interpolation.py
@@ -1,7 +1,13 @@
 # coding: utf-8
 # Copyright 2018 Yaman Güçlü
 
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
+    
 import numpy as np
 import pytest
 import time
diff --git a/psydac/fem/tests/test_splines_par.py b/psydac/fem/tests/test_splines_par.py
index c1dae5afe..4c62b7734 100644
--- a/psydac/fem/tests/test_splines_par.py
+++ b/psydac/fem/tests/test_splines_par.py
@@ -9,7 +9,12 @@
 from psydac.ddm.cart    import DomainDecomposition
 
 from numpy  import linspace
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 def test_2d_1():
 
diff --git a/psydac/linalg/block.py b/psydac/linalg/block.py
index b9fdc7d4b..8e9ce7a48 100644
--- a/psydac/linalg/block.py
+++ b/psydac/linalg/block.py
@@ -1064,7 +1064,13 @@ def compute_interface_matrices_transpose(self):
         if not self.codomain.parallel:
             return blocks, blocks_T
 
-        from mpi4py import MPI
+        from typing import TYPE_CHECKING
+
+        if TYPE_CHECKING:
+            from mpi4py import MPI
+        else:
+            from psydac.ddm.mpi import mpi as MPI
+            
         from psydac.linalg.stencil import StencilInterfaceMatrix
 
         if not isinstance(self.codomain, BlockVectorSpace):
diff --git a/psydac/linalg/stencil.py b/psydac/linalg/stencil.py
index 4c62139fc..c8fac007b 100644
--- a/psydac/linalg/stencil.py
+++ b/psydac/linalg/stencil.py
@@ -9,7 +9,12 @@
 
 from types        import MappingProxyType
 from scipy.sparse import coo_matrix, diags as sp_diags
-from mpi4py       import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.linalg.basic  import VectorSpace, Vector, LinearOperator
 from psydac.ddm.cart      import find_mpi_type, CartDecomposition, InterfaceCartDecomposition
diff --git a/psydac/linalg/tests/test_block.py b/psydac/linalg/tests/test_block.py
index cf887da29..880f316a6 100644
--- a/psydac/linalg/tests/test_block.py
+++ b/psydac/linalg/tests/test_block.py
@@ -4,6 +4,12 @@
 import numpy as np
 from scipy.sparse import csr_matrix
 from random import random, seed
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.linalg.direct_solvers import SparseSolver
 from psydac.linalg.stencil        import StencilVectorSpace, StencilVector, StencilMatrix
@@ -999,8 +1005,6 @@ def test_block_linear_operator_parallel_dot( dtype, n1, n2, p1, p2, P1, P2 ):
     # set seed for reproducibility
     seed(n1*n2*p1*p2)
 
-    from mpi4py       import MPI
-
     comm = MPI.COMM_WORLD
     D = DomainDecomposition([n1,n2], periods=[P1,P2], comm=comm)
 
@@ -1130,7 +1134,6 @@ def test_block_linear_operator_parallel_dot( dtype, n1, n2, p1, p2, P1, P2 ):
 def test_block_vector_2d_parallel_array_to_psydac(dtype, n1, n2, p1, p2, s1, s2, P1, P2):
     npts = [n1, n2]   
 
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -1221,7 +1224,6 @@ def test_block_vector_2d_parallel_topetsc( dtype, n1, n2, p1, p2, P1, P2 ):
     # set seed for reproducibility
     seed(n1*n2*p1*p2)
 
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     D = DomainDecomposition([n1,n2], periods=[P1,P2], comm=comm)
@@ -1269,7 +1271,6 @@ def test_block_vector_2d_parallel_topetsc( dtype, n1, n2, p1, p2, P1, P2 ):
 def test_block_linear_operator_1d_parallel_topetsc( dtype, n1, p1, P1):
     # set seed for reproducibility
     seed(n1*p1)
-    from mpi4py import MPI
 
     D = DomainDecomposition([n1], periods=[P1], comm=MPI.COMM_WORLD)
 
@@ -1343,7 +1344,6 @@ def test_block_linear_operator_1d_parallel_topetsc( dtype, n1, p1, P1):
 def test_block_linear_operator_2d_parallel_topetsc( dtype, n1, n2, p1, p2, P1, P2):
     # set seed for reproducibility
     seed(n1*n2*p1*p2)
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     D = DomainDecomposition([n1,n2], periods=[P1,P2], comm=comm)
@@ -1427,9 +1427,7 @@ def test_block_matrix_operator_parallel_dot_backend( dtype, n1, n2, p1, p2, P1,
     else:
         factor = 1
     # set seed for reproducibility
-
-    from mpi4py       import MPI
-
+    
     comm = MPI.COMM_WORLD
     D = DomainDecomposition([n1,n2], periods=[P1,P2], comm=comm)
 
diff --git a/psydac/linalg/tests/test_fft.py b/psydac/linalg/tests/test_fft.py
index a9bcef459..d3fa6fed7 100644
--- a/psydac/linalg/tests/test_fft.py
+++ b/psydac/linalg/tests/test_fft.py
@@ -1,7 +1,12 @@
 import pytest
 import scipy.fft as scifft
 import numpy as np
-from mpi4py import MPI
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.linalg.fft import *
 from psydac.ddm.cart               import DomainDecomposition, CartDecomposition
diff --git a/psydac/linalg/tests/test_stencil_interface_matrix.py b/psydac/linalg/tests/test_stencil_interface_matrix.py
index 60693952c..499f3a61b 100644
--- a/psydac/linalg/tests/test_stencil_interface_matrix.py
+++ b/psydac/linalg/tests/test_stencil_interface_matrix.py
@@ -226,7 +226,13 @@ def test_stencil_interface_matrix_3d_serial_init(dtype, n1, n2, n3, p1, p2, p3,
 @pytest.mark.parallel
 def test_stencil_interface_matrix_2d_parallel_dot(n1, n2, p1, p2, expected):
 
-    from mpi4py              import MPI
+    from typing import TYPE_CHECKING
+
+    if TYPE_CHECKING:
+        from mpi4py import MPI
+    else:
+        from psydac.ddm.mpi import mpi as MPI
+        
     from psydac.ddm.cart     import MultiPatchDomainDecomposition, CartDecomposition, create_interfaces_cart
     from psydac.linalg.block import BlockVectorSpace, BlockVector, BlockLinearOperator
 
diff --git a/psydac/linalg/tests/test_stencil_vector.py b/psydac/linalg/tests/test_stencil_vector.py
index 0983edf80..2f3a78ac8 100644
--- a/psydac/linalg/tests/test_stencil_vector.py
+++ b/psydac/linalg/tests/test_stencil_vector.py
@@ -2,6 +2,12 @@
 
 import pytest
 import numpy as np
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.linalg.stencil import StencilVectorSpace, StencilVector, StencilMatrix
 from psydac.linalg.utilities import array_to_psydac, petsc_to_psydac
@@ -528,7 +534,6 @@ def test_stencil_vector_2d_serial_update_ghost_region_interior(dtype, n1, n2, p1
 @pytest.mark.parallel
 def test_stencil_vector_1d_parallel_init(dtype, n1, p1, s1, P1=True):
 
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -564,7 +569,6 @@ def test_stencil_vector_1d_parallel_init(dtype, n1, p1, s1, P1=True):
 @pytest.mark.parallel
 def test_stencil_vector_2d_parallel_init(dtype, n1, n2, p1, p2, s1, s2, P1=True, P2=False):
 
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -602,7 +606,7 @@ def test_stencil_vector_2d_parallel_init(dtype, n1, n2, p1, p2, s1, s2, P1=True,
 @pytest.mark.parallel
 @pytest.mark.petsc
 def test_stencil_vector_2d_parallel_topetsc(dtype, n1, n2, p1, p2, s1, s2, P1, P2):
-    from mpi4py import MPI
+
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -645,7 +649,7 @@ def test_stencil_vector_2d_parallel_topetsc(dtype, n1, n2, p1, p2, s1, s2, P1, P
 @pytest.mark.parallel
 @pytest.mark.petsc
 def test_stencil_vector_1d_parallel_topetsc(dtype, n1, p1, s1, P1):
-    from mpi4py import MPI
+
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -696,7 +700,7 @@ def test_stencil_vector_1d_parallel_topetsc(dtype, n1, p1, s1, P1):
 @pytest.mark.parallel
 @pytest.mark.petsc
 def test_stencil_vector_3d_parallel_topetsc(dtype, n1, n2, n3, p1, p2, p3, s1, s2, s3, P1, P2, P3):
-    from mpi4py import MPI
+
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -746,7 +750,6 @@ def test_stencil_vector_3d_parallel_topetsc(dtype, n1, n2, n3, p1, p2, p3, s1, s
 @pytest.mark.parallel
 def test_stencil_vector_3d_parallel_init(dtype, n1, n2, n3, p1, p2, p3, s1, s2, s3, P1=True, P2=False, P3=True):
 
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -783,8 +786,6 @@ def test_stencil_vector_3d_parallel_init(dtype, n1, n2, n3, p1, p2, p3, s1, s2,
 @pytest.mark.parallel
 def test_stencil_vector_2d_parallel_toarray(dtype, n1, n2, p1, p2, s1, s2, P1=True, P2=False):
     # Create domain decomposition
-    from mpi4py import MPI
-
     comm = MPI.COMM_WORLD
     D = DomainDecomposition([n1, n2], periods=[P1, P2], comm=comm)
 
@@ -853,7 +854,6 @@ def test_stencil_vector_2d_parallel_toarray(dtype, n1, n2, p1, p2, s1, s2, P1=Tr
 def test_stencil_vector_2d_parallel_array_to_psydac(dtype, n1, n2, p1, p2, s1, s2, P1, P2):
     npts = [n1, n2]   
 
-    from mpi4py import MPI
     comm = MPI.COMM_WORLD
 
     # Create domain decomposition
@@ -909,7 +909,6 @@ def test_stencil_vector_2d_parallel_array_to_psydac(dtype, n1, n2, p1, p2, s1, s
 @pytest.mark.parametrize('s2', [1])
 @pytest.mark.parallel
 def test_stencil_vector_2d_parallel_dot(dtype, n1, n2, p1, p2, s1, s2, P1=True, P2=False):
-    from mpi4py import MPI
 
     comm = MPI.COMM_WORLD
     # Create domain decomposition
@@ -977,7 +976,6 @@ def test_stencil_vector_2d_parallel_dot(dtype, n1, n2, p1, p2, s1, s2, P1=True,
 @pytest.mark.parametrize('s3', [1])
 @pytest.mark.parallel
 def test_stencil_vector_3d_parallel_dot(dtype, n1, n2, n3, p1, p2, p3, s1, s2, s3, P1=True, P2=False, P3=True):
-    from mpi4py import MPI
 
     comm = MPI.COMM_WORLD
     # Create domain decomposition
diff --git a/psydac/linalg/tests/test_stencil_vector_space.py b/psydac/linalg/tests/test_stencil_vector_space.py
index 2ef09b26e..31388fe2e 100644
--- a/psydac/linalg/tests/test_stencil_vector_space.py
+++ b/psydac/linalg/tests/test_stencil_vector_space.py
@@ -1,5 +1,11 @@
 import pytest
 import numpy as np
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mpi4py import MPI
+else:
+    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.linalg.stencil import StencilVectorSpace, StencilVector
 from psydac.ddm.cart import DomainDecomposition, CartDecomposition, find_mpi_type
@@ -279,8 +285,6 @@ def test_stencil_vector_space_2D_serial_set_interface(dtype, n1, n2, p1, p2, s1,
 
 def test_stencil_vector_space_1d_parallel_init(dtype, n1, p1, s1, P1):
 
-    from mpi4py import MPI
-
     comm = MPI.COMM_WORLD
     # Create domain decomposition
     D = DomainDecomposition([n1], periods=[P1], comm=comm)
@@ -326,8 +330,6 @@ def test_stencil_vector_space_1d_parallel_init(dtype, n1, p1, s1, P1):
 
 def test_stencil_vector_space_2d_parallel_init(dtype, n1, n2, p1, p2, s1, s2, P1, P2):
 
-    from mpi4py import MPI
-
     comm = MPI.COMM_WORLD
     # Create domain decomposition
     D = DomainDecomposition([n1, n2], periods=[P1, P2], comm=comm)
@@ -373,8 +375,6 @@ def test_stencil_vector_space_2d_parallel_init(dtype, n1, n2, p1, p2, s1, s2, P1
 
 def test_stencil_vector_space_3d_parallel_init(dtype, n1, n2, n3, p1, p2, p3, s1, s2, s3, P1=True, P2=False, P3=True):
 
-    from mpi4py import MPI
-
     comm = MPI.COMM_WORLD
     # Create domain decomposition
     D = DomainDecomposition([n1, n2, n3], periods=[P1, P2, P3], comm=comm)
@@ -413,8 +413,6 @@ def test_stencil_vector_space_3d_parallel_init(dtype, n1, n2, n3, p1, p2, p3, s1
 
 def test_stencil_vector_space_2D_parallel_parent(dtype, n1, n2, P1=True, P2=False):
 
-    from mpi4py import MPI
-
     comm = MPI.COMM_WORLD
     # Create domain decomposition
     D = DomainDecomposition([n1, n2], periods=[P1, P2], comm=comm)

From 04e3980c10eba5ba371491b53c65eb1c4f523b70 Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 07:28:37 +0200
Subject: [PATCH 04/13] make mpi4py an optional dependency; run tests without
 mpi too

---
 .github/workflows/testing.yml | 18 ++++++++++++------
 psydac/ddm/mpi.py             |  3 ---
 pyproject.toml                |  4 +++-
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 98d80ceb0..897eebe89 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -328,9 +328,9 @@ jobs:
       #       f = h5py.File('parallel_test.hdf5', 'w', driver='mpio', comm=MPI.COMM_WORLD)
       #       print(f)"
 
-      - name: Install project
+      - name: Install project without mpi
         run: |
-          python -m pip install ".[test]" --no-cache-dir
+          python -m pip install ".[test,mpi]" --no-cache-dir
           python -m pip freeze
       
       - name: Compile psydac kernels
@@ -362,15 +362,20 @@ jobs:
         run: |
           python -m pytest -n auto --pyargs psydac -m "not parallel and not petsc"
 
-      - name: Run MPI tests with Pytest
+      - name: Run single-process PETSc tests with Pytest
         working-directory: ./pytest
         run: |
-          python mpi_tester.py --mpirun="mpiexec -n 4 ${MPI_OPTS}" --pyargs psydac -m "parallel and not petsc"
+          python -m pytest -n auto --pyargs psydac -m "not parallel and petsc"
 
-      - name: Run single-process PETSc tests with Pytest
+      - name: Install project with mpi
+        run: |
+          python -m pip install ".[mpi]" 
+          python -m pip freeze
+
+      - name: Run MPI tests with Pytest
         working-directory: ./pytest
         run: |
-          python -m pytest -n auto --pyargs psydac -m "not parallel and petsc"
+          python mpi_tester.py --mpirun="mpiexec -n 4 ${MPI_OPTS}" --pyargs psydac -m "parallel and not petsc"
 
       - name: Run MPI PETSc tests with Pytest
         working-directory: ./pytest
@@ -381,6 +386,7 @@ jobs:
         if: always()
         run: |
           rm -rf pytest
+  
   test_struphy:
     runs-on: ${{ matrix.os }}
     strategy:
diff --git a/psydac/ddm/mpi.py b/psydac/ddm/mpi.py
index d4a31a118..dc2161083 100644
--- a/psydac/ddm/mpi.py
+++ b/psydac/ddm/mpi.py
@@ -66,9 +66,6 @@ def dummy(*args, **kwargs):
     @property
     def COMM_WORLD(self):
         return MockComm()
-    
-    class Comm:
-        x = None
 
     # def comm_Get_rank(self):
     #     return 0
diff --git a/pyproject.toml b/pyproject.toml
index 3e45a3bde..6ad294fa3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -31,7 +31,6 @@ dependencies = [
 
     # Our packages from PyPi
     'pyccel >= 2.0.1',
-    'mpi4py >= 4',
     'h5py',
 
     # When pyccel is run in parallel with MPI, it uses tblib to pickle
@@ -45,6 +44,9 @@ test = [
     'pytest >= 4.5',
     'pytest-xdist >= 1.16',
 ]
+mpi = [
+    'mpi4py >= 4',
+]
 
 [project.urls]
 Homepage      = "https://github.com/pyccel/psydac"

From 1eb029704c9e6ac5e02db451944b089bc20e70c3 Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 07:44:45 +0200
Subject: [PATCH 05/13] add forgotton change

---
 .github/workflows/testing.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 897eebe89..d1ac0757b 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -330,7 +330,7 @@ jobs:
 
       - name: Install project without mpi
         run: |
-          python -m pip install ".[test,mpi]" --no-cache-dir
+          python -m pip install ".[test]" --no-cache-dir
           python -m pip freeze
       
       - name: Compile psydac kernels

From af5279aadba3d59c851a2d0174dc28eaee05722b Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 07:50:59 +0200
Subject: [PATCH 06/13] change version to 2.5.0 for last release still on
 GitLab

---
 pyproject.toml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 6ad294fa3..e7717ce09 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name            = "psydac"
-version         = "2.4.5.dev0"
+version         = "2.5.0.dev0"
 description     = "Python package for isogeometric analysis (IGA)"
 readme          = "README.md"
 requires-python = ">= 3.10"

From e81aee44adff6582573e631d24ef535ccb6556f5 Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 09:14:34 +0200
Subject: [PATCH 07/13] install Struphy from branch 467-no-mpi; perform Struphy
 unit tests on 1 and 2 processes

---
 .github/workflows/testing.yml | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index d1ac0757b..73c8e968a 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -475,7 +475,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
 
-      - name: Install project
+      - name: Install project without mpi
         run: |
           python -m pip install ".[test]" --no-cache-dir
           python -m pip freeze
@@ -485,11 +485,11 @@ jobs:
           echo "PSYDAC_DIR=$GITHUB_WORKSPACE" >> $GITHUB_ENV
           echo "STRUPHY_DIR=$GITHUB_WORKSPACE/struphy" >> $GITHUB_ENV
 
-      - name: Clone struphy from GitLab #TODO: Set branch to devel
+      - name: Clone struphy from GitLab #TODO: Set branch to 467-no-mpi
         run: |
-          git clone https://gitlab.mpcdf.mpg.de/struphy/struphy.git $STRUPHY_DIR
+          git clone https://gitlab.mpcdf.mpg.de/struphy/struphy.git@467-no-mpi $STRUPHY_DIR
       
-      - name: Install struphy
+      - name: Install struphy without mpi
         working-directory: ${{ env.STRUPHY_DIR }}
         run: |
           echo "Psydac location for this branch"
@@ -526,6 +526,16 @@ jobs:
         run: |
             struphy test models --fast
 
+      - name: Install mpi4py
+        working-directory: ${{ env.STRUPHY_DIR }}
+        run: |
+            pip install -U mpi4py
+
+      - name: Run struphy unit tests with mpi
+        working-directory: ${{ env.STRUPHY_DIR }}
+        run: |
+            struphy test unit --mpi 2
+
       - name: Remove test directory
         if: always()
         run: |

From c423b57715702ba47ddeadc9eeca2d7386a8b60c Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 09:21:52 +0200
Subject: [PATCH 08/13] checkout correct Struphy branch 467-no-mpi

---
 .github/workflows/testing.yml | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 73c8e968a..85d80a312 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -487,7 +487,7 @@ jobs:
 
       - name: Clone struphy from GitLab #TODO: Set branch to 467-no-mpi
         run: |
-          git clone https://gitlab.mpcdf.mpg.de/struphy/struphy.git@467-no-mpi $STRUPHY_DIR
+          git clone https://gitlab.mpcdf.mpg.de/struphy/struphy.git $STRUPHY_DIR
       
       - name: Install struphy without mpi
         working-directory: ${{ env.STRUPHY_DIR }}
@@ -495,6 +495,7 @@ jobs:
           echo "Psydac location for this branch"
           pip show psydac
           pip uninstall psydac -y
+          git checkout 467-no-mpi
           python -m pip install ".[phys]" --no-cache-dir
           echo "Psydac location after installing struphy"
           pip show psydac

From 5115551105e1301b98a2977a1731c0d5986902ea Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 13:37:16 +0200
Subject: [PATCH 09/13] correct TODO to devel

---
 .github/workflows/testing.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 85d80a312..331824207 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -485,11 +485,11 @@ jobs:
           echo "PSYDAC_DIR=$GITHUB_WORKSPACE" >> $GITHUB_ENV
           echo "STRUPHY_DIR=$GITHUB_WORKSPACE/struphy" >> $GITHUB_ENV
 
-      - name: Clone struphy from GitLab #TODO: Set branch to 467-no-mpi
+      - name: Clone struphy from GitLab
         run: |
           git clone https://gitlab.mpcdf.mpg.de/struphy/struphy.git $STRUPHY_DIR
       
-      - name: Install struphy without mpi
+      - name: Install struphy without mpi #TODO: Set branch to devel
         working-directory: ${{ env.STRUPHY_DIR }}
         run: |
           echo "Psydac location for this branch"

From 34f223f377459c6b5d4c76c79e3c70b4daa8a362 Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Fri, 17 Oct 2025 13:44:49 +0200
Subject: [PATCH 10/13] remove the unneccessary if TYPE_CHECKING thing from all
 files, except mpi.py

---
 mpi_tester.py                                     | 15 ++-------------
 psydac/ddm/blocking_data_exchanger.py             |  7 +------
 psydac/ddm/cart.py                                |  7 +------
 psydac/ddm/interface_data_exchanger.py            |  7 +------
 psydac/ddm/mpi.py                                 |  4 +---
 psydac/ddm/nonblocking_data_exchanger.py          |  7 +------
 psydac/ddm/tests/test_cart_1d.py                  |  8 +-------
 psydac/ddm/tests/test_cart_2d.py                  |  8 +-------
 psydac/ddm/tests/test_cart_3d.py                  |  8 +-------
 psydac/ddm/tests/test_multicart_2d.py             |  9 ++-------
 psydac/fem/partitioning.py                        |  6 ------
 psydac/fem/tensor.py                              |  7 +------
 psydac/fem/tests/test_spline_interpolation.py     |  7 +------
 psydac/fem/tests/test_splines_par.py              |  7 +------
 psydac/linalg/block.py                            |  8 +-------
 psydac/linalg/stencil.py                          |  7 +------
 psydac/linalg/tests/test_block.py                 |  7 +------
 psydac/linalg/tests/test_fft.py                   |  7 +------
 .../linalg/tests/test_stencil_interface_matrix.py |  8 +-------
 psydac/linalg/tests/test_stencil_vector.py        |  7 +------
 psydac/linalg/tests/test_stencil_vector_space.py  |  7 +------
 21 files changed, 22 insertions(+), 136 deletions(-)

diff --git a/mpi_tester.py b/mpi_tester.py
index c6eb32a8f..e7f718a69 100644
--- a/mpi_tester.py
+++ b/mpi_tester.py
@@ -101,12 +101,7 @@ def MPITest(commsize):
     def test_stuff(comm):
         pass
     """
-    from typing import TYPE_CHECKING
-
-    if TYPE_CHECKING:
-        from mpi4py import MPI
-    else:
-        from psydac.ddm.mpi import mpi as MPI
+    from psydac.ddm.mpi import mpi as MPI
         
     if not isinstance(commsize, (tuple, list)):
         commsize = (commsize,)
@@ -188,13 +183,7 @@ def __init__(self):
     #---------------------------------------------------------------------------
     @property
     def comm(self):
-        from typing import TYPE_CHECKING
-
-        if TYPE_CHECKING:
-            from mpi4py import MPI
-        else:
-            from psydac.ddm.mpi import mpi as MPI
-            
+        from psydac.ddm.mpi import mpi as MPI
         return MPI.COMM_WORLD
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/blocking_data_exchanger.py b/psydac/ddm/blocking_data_exchanger.py
index df9df0c3e..0a8c4759a 100644
--- a/psydac/ddm/blocking_data_exchanger.py
+++ b/psydac/ddm/blocking_data_exchanger.py
@@ -1,12 +1,7 @@
 # coding: utf-8
 
 import numpy as np
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
+from psydac.ddm.mpi import mpi as MPI
 
 from .cart import CartDecomposition, find_mpi_type
 from .basic import CartDataExchanger
diff --git a/psydac/ddm/cart.py b/psydac/ddm/cart.py
index b4c00de01..229f4fb0d 100644
--- a/psydac/ddm/cart.py
+++ b/psydac/ddm/cart.py
@@ -3,13 +3,8 @@
 import os
 import numpy as np
 from itertools import product
-from typing import TYPE_CHECKING
 
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
-    
+from psydac.ddm.mpi import mpi as MPI
 from psydac.ddm.mpi import MockMPI
 from psydac.ddm.partition import compute_dims, partition_procs_per_patch
 
diff --git a/psydac/ddm/interface_data_exchanger.py b/psydac/ddm/interface_data_exchanger.py
index fb74ab4f7..ef3a209c8 100644
--- a/psydac/ddm/interface_data_exchanger.py
+++ b/psydac/ddm/interface_data_exchanger.py
@@ -1,11 +1,6 @@
 # coding: utf-8
 
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
+from psydac.ddm.mpi import mpi as MPI
 
 from .cart import InterfaceCartDecomposition, find_mpi_type
 
diff --git a/psydac/ddm/mpi.py b/psydac/ddm/mpi.py
index dc2161083..7c9abf240 100644
--- a/psydac/ddm/mpi.py
+++ b/psydac/ddm/mpi.py
@@ -97,6 +97,4 @@ def COMM_WORLD(self):
 
     mpi = MPI
 else:
-    mpi = mpi_wrapper.MPI
-
-print(f"{mpi = }")
\ No newline at end of file
+    mpi = mpi_wrapper.MPI
\ No newline at end of file
diff --git a/psydac/ddm/nonblocking_data_exchanger.py b/psydac/ddm/nonblocking_data_exchanger.py
index 88a6ae334..ecfc15730 100644
--- a/psydac/ddm/nonblocking_data_exchanger.py
+++ b/psydac/ddm/nonblocking_data_exchanger.py
@@ -2,13 +2,8 @@
 
 import numpy as np
 from itertools import product
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
+from psydac.ddm.mpi import mpi as MPI
 from .cart import CartDecomposition, find_mpi_type
 from .basic import CartDataExchanger
 
diff --git a/psydac/ddm/tests/test_cart_1d.py b/psydac/ddm/tests/test_cart_1d.py
index 55d7b7011..ea5446da2 100644
--- a/psydac/ddm/tests/test_cart_1d.py
+++ b/psydac/ddm/tests/test_cart_1d.py
@@ -11,13 +11,7 @@
 def run_cart_1d( data_exchanger_type, verbose=False ):
 
     import numpy as np
-    from typing import TYPE_CHECKING
-
-    if TYPE_CHECKING:
-        from mpi4py import MPI
-    else:
-        from psydac.ddm.mpi import mpi as MPI
-        
+    from psydac.ddm.mpi import mpi as MPI
     from psydac.ddm.cart import DomainDecomposition, CartDecomposition
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/tests/test_cart_2d.py b/psydac/ddm/tests/test_cart_2d.py
index f2c24260b..3f21af8ad 100644
--- a/psydac/ddm/tests/test_cart_2d.py
+++ b/psydac/ddm/tests/test_cart_2d.py
@@ -9,13 +9,7 @@
 def run_cart_2d( data_exchanger_type, verbose=False , nprocs=None, reverse_axis=None):
 
     import numpy as np
-    from typing import TYPE_CHECKING
-
-    if TYPE_CHECKING:
-        from mpi4py import MPI
-    else:
-        from psydac.ddm.mpi import mpi as MPI
-        
+    from psydac.ddm.mpi import mpi as MPI  
     from psydac.ddm.cart import DomainDecomposition, CartDecomposition
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/tests/test_cart_3d.py b/psydac/ddm/tests/test_cart_3d.py
index 00ba32b88..7f86a32f2 100644
--- a/psydac/ddm/tests/test_cart_3d.py
+++ b/psydac/ddm/tests/test_cart_3d.py
@@ -9,13 +9,7 @@
 def run_cart_3d( data_exchanger_type, verbose=False ):
 
     import numpy as np
-    from typing import TYPE_CHECKING
-
-    if TYPE_CHECKING:
-        from mpi4py import MPI
-    else:
-        from psydac.ddm.mpi import mpi as MPI
-        
+    from psydac.ddm.mpi import mpi as MPI 
     from psydac.ddm.cart import DomainDecomposition, CartDecomposition
 
     #---------------------------------------------------------------------------
diff --git a/psydac/ddm/tests/test_multicart_2d.py b/psydac/ddm/tests/test_multicart_2d.py
index 062749430..4d8f57917 100644
--- a/psydac/ddm/tests/test_multicart_2d.py
+++ b/psydac/ddm/tests/test_multicart_2d.py
@@ -36,13 +36,8 @@ def get_plus_starts_ends(minus_starts, minus_ends, minus_npts, plus_npts, minus_
 #===============================================================================
 def run_carts_2d():
     import numpy as np
-    from typing import TYPE_CHECKING
-
-    if TYPE_CHECKING:
-        from mpi4py import MPI
-    else:
-        from psydac.ddm.mpi import mpi as MPI
-        
+    
+    from psydac.ddm.mpi import mpi as MPI
     from psydac.ddm.cart import MultiPatchDomainDecomposition, CartDecomposition, create_interfaces_cart
     from psydac.ddm.blocking_data_exchanger  import BlockingCartDataExchanger
     from psydac.ddm.interface_data_exchanger import InterfaceCartDataExchanger
diff --git a/psydac/fem/partitioning.py b/psydac/fem/partitioning.py
index 804cf87e2..de3a3acaf 100644
--- a/psydac/fem/partitioning.py
+++ b/psydac/fem/partitioning.py
@@ -2,12 +2,6 @@
 import os
 
 import numpy as np
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
 from psydac.ddm.cart       import CartDecomposition, InterfaceCartDecomposition, create_interfaces_cart
 from psydac.core.bsplines  import elements_spans
diff --git a/psydac/fem/tensor.py b/psydac/fem/tensor.py
index 02203922c..70f849c69 100644
--- a/psydac/fem/tensor.py
+++ b/psydac/fem/tensor.py
@@ -5,12 +5,7 @@
 of compact support
 
 """
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
+from psydac.ddm.mpi import mpi as MPI
     
 import numpy as np
 import itertools
diff --git a/psydac/fem/tests/test_spline_interpolation.py b/psydac/fem/tests/test_spline_interpolation.py
index b2777a46b..b572e45b8 100644
--- a/psydac/fem/tests/test_spline_interpolation.py
+++ b/psydac/fem/tests/test_spline_interpolation.py
@@ -1,12 +1,7 @@
 # coding: utf-8
 # Copyright 2018 Yaman Güçlü
 
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
+from psydac.ddm.mpi import mpi as MPI
     
 import numpy as np
 import pytest
diff --git a/psydac/fem/tests/test_splines_par.py b/psydac/fem/tests/test_splines_par.py
index 4c62b7734..081d26074 100644
--- a/psydac/fem/tests/test_splines_par.py
+++ b/psydac/fem/tests/test_splines_par.py
@@ -7,14 +7,9 @@
 from psydac.fem.tensor  import TensorFemSpace
 from psydac.fem.vector  import VectorFemSpace
 from psydac.ddm.cart    import DomainDecomposition
+from psydac.ddm.mpi import mpi as MPI
 
 from numpy  import linspace
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
 def test_2d_1():
 
diff --git a/psydac/linalg/block.py b/psydac/linalg/block.py
index 8e9ce7a48..7db84a9f4 100644
--- a/psydac/linalg/block.py
+++ b/psydac/linalg/block.py
@@ -1064,13 +1064,7 @@ def compute_interface_matrices_transpose(self):
         if not self.codomain.parallel:
             return blocks, blocks_T
 
-        from typing import TYPE_CHECKING
-
-        if TYPE_CHECKING:
-            from mpi4py import MPI
-        else:
-            from psydac.ddm.mpi import mpi as MPI
-            
+        from psydac.ddm.mpi import mpi as MPI
         from psydac.linalg.stencil import StencilInterfaceMatrix
 
         if not isinstance(self.codomain, BlockVectorSpace):
diff --git a/psydac/linalg/stencil.py b/psydac/linalg/stencil.py
index c8fac007b..85b03c4e4 100644
--- a/psydac/linalg/stencil.py
+++ b/psydac/linalg/stencil.py
@@ -9,13 +9,8 @@
 
 from types        import MappingProxyType
 from scipy.sparse import coo_matrix, diags as sp_diags
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
+from psydac.ddm.mpi import mpi as MPI
 from psydac.linalg.basic  import VectorSpace, Vector, LinearOperator
 from psydac.ddm.cart      import find_mpi_type, CartDecomposition, InterfaceCartDecomposition
 from psydac.ddm.utilities import get_data_exchanger
diff --git a/psydac/linalg/tests/test_block.py b/psydac/linalg/tests/test_block.py
index 880f316a6..00badb580 100644
--- a/psydac/linalg/tests/test_block.py
+++ b/psydac/linalg/tests/test_block.py
@@ -4,13 +4,8 @@
 import numpy as np
 from scipy.sparse import csr_matrix
 from random import random, seed
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
+from psydac.ddm.mpi import mpi as MPI
 from psydac.linalg.direct_solvers import SparseSolver
 from psydac.linalg.stencil        import StencilVectorSpace, StencilVector, StencilMatrix
 from psydac.linalg.block          import BlockVectorSpace, BlockVector
diff --git a/psydac/linalg/tests/test_fft.py b/psydac/linalg/tests/test_fft.py
index d3fa6fed7..014ce95eb 100644
--- a/psydac/linalg/tests/test_fft.py
+++ b/psydac/linalg/tests/test_fft.py
@@ -1,13 +1,8 @@
 import pytest
 import scipy.fft as scifft
 import numpy as np
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
+from psydac.ddm.mpi import mpi as MPI
 from psydac.linalg.fft import *
 from psydac.ddm.cart               import DomainDecomposition, CartDecomposition
 from psydac.linalg.stencil import StencilVector
diff --git a/psydac/linalg/tests/test_stencil_interface_matrix.py b/psydac/linalg/tests/test_stencil_interface_matrix.py
index 499f3a61b..b0fa74f08 100644
--- a/psydac/linalg/tests/test_stencil_interface_matrix.py
+++ b/psydac/linalg/tests/test_stencil_interface_matrix.py
@@ -226,13 +226,7 @@ def test_stencil_interface_matrix_3d_serial_init(dtype, n1, n2, n3, p1, p2, p3,
 @pytest.mark.parallel
 def test_stencil_interface_matrix_2d_parallel_dot(n1, n2, p1, p2, expected):
 
-    from typing import TYPE_CHECKING
-
-    if TYPE_CHECKING:
-        from mpi4py import MPI
-    else:
-        from psydac.ddm.mpi import mpi as MPI
-        
+    from psydac.ddm.mpi import mpi as MPI
     from psydac.ddm.cart     import MultiPatchDomainDecomposition, CartDecomposition, create_interfaces_cart
     from psydac.linalg.block import BlockVectorSpace, BlockVector, BlockLinearOperator
 
diff --git a/psydac/linalg/tests/test_stencil_vector.py b/psydac/linalg/tests/test_stencil_vector.py
index 2f3a78ac8..3b95419bd 100644
--- a/psydac/linalg/tests/test_stencil_vector.py
+++ b/psydac/linalg/tests/test_stencil_vector.py
@@ -2,13 +2,8 @@
 
 import pytest
 import numpy as np
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
+from psydac.ddm.mpi import mpi as MPI
 from psydac.linalg.stencil import StencilVectorSpace, StencilVector, StencilMatrix
 from psydac.linalg.utilities import array_to_psydac, petsc_to_psydac
 from psydac.ddm.cart import DomainDecomposition, CartDecomposition
diff --git a/psydac/linalg/tests/test_stencil_vector_space.py b/psydac/linalg/tests/test_stencil_vector_space.py
index 31388fe2e..7ada7ca50 100644
--- a/psydac/linalg/tests/test_stencil_vector_space.py
+++ b/psydac/linalg/tests/test_stencil_vector_space.py
@@ -1,12 +1,7 @@
 import pytest
 import numpy as np
-from typing import TYPE_CHECKING
-
-if TYPE_CHECKING:
-    from mpi4py import MPI
-else:
-    from psydac.ddm.mpi import mpi as MPI
 
+from psydac.ddm.mpi import mpi as MPI
 from psydac.linalg.stencil import StencilVectorSpace, StencilVector
 from psydac.ddm.cart import DomainDecomposition, CartDecomposition, find_mpi_type
 

From 8a7326330712ea4108566843029785a1054af6d3 Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Mon, 20 Oct 2025 08:14:19 +0200
Subject: [PATCH 11/13] set mpi_enabled to True if mpi4py is installed, TODO:
 check if it runs under mpirun

---
 psydac/ddm/mpi.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/psydac/ddm/mpi.py b/psydac/ddm/mpi.py
index 7c9abf240..40f29ef06 100644
--- a/psydac/ddm/mpi.py
+++ b/psydac/ddm/mpi.py
@@ -80,7 +80,7 @@ def COMM_WORLD(self):
     _comm = MPI.COMM_WORLD
     rank = _comm.Get_rank()
     size = _comm.Get_size()
-    mpi_enabled = size > 1
+    mpi_enabled = True
 except ImportError:
     # mpi4py not installed
     mpi_enabled = False

From 6f632dc34d426ea2bc8e6872ef449d179b642f1d Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Mon, 20 Oct 2025 08:48:50 +0200
Subject: [PATCH 12/13] test with updated struphy branch


From 9a4ea9a02600d7b046620866826a9e6c77685e6c Mon Sep 17 00:00:00 2001
From: Stefan Possanner <stefan.possanner@ipp.mpg.de>
Date: Mon, 20 Oct 2025 09:53:28 +0200
Subject: [PATCH 13/13] test with updated struphy branch