Information for C++ Developers

The dune Python bindings rely on just in time (JIT) compilation which takes place in a special dune module dune-py. Which each C++ type a Python module is generated there. One can obtain information about and manipulate this module using the dune main script:

python -m dune
usage: dune [-h] {info,configure,list,remove,fix-dunepy,dunetype,checkbuilddirs}

remove              Remove generated modules
info                Print information about dune-py
list                List all generated modules
dunetype            Show dune types for given modules

fix-dunepy          Find inconsistencies in dune-py and try to fix automatically. This will potentially delete all generated modules.
configure           Tag dune-py to be reconfigured before next use
checkbuilddirs      (internal use) Check build directories

Probably the most important option here is remove which simplifies removing specific modules from dune-py. This is important to debug C++ code because a module can then be recompiled with debugging compiler flags.

python -m dune remove
usage: dune remove [-h] [--beforedate] [modules [modules ...]]

positional arguments:
  modules       Patterns of modules ("\*.cc" and dune-py path is added to each argument) or "all"

optional arguments:
  -h, --help    show this help message and exit
  --beforedate  Instead of a pattern provide a date to remove all modules not having been loaded
                after that date

In addition to providing a full module (without extension and path), one can provide the module prefix (e.g. hierarchicalgrid) and all modules with this prefix will be removed. If is quite easy to find the module name from a generated dune object in Python by using the __module__ magic attribute. The following script outputs

from dune.grid import structuredGrid
view = structuredGrid([0,0],[1,1],[10,10])
print(view.__module__)

dune.generated.hierarchicalgrid_966e2a5c8356c5b278ccd3acad180f0a. So removing this module can be achieved by calling

python -m dune remove hierarchicalgrid_966e2a5c8356c5b278ccd3acad180f0a

There are two options to compile a module that has not been generated yet (e.g. was removed) with different flags. Either by setting the CXXFLAGS environment variable, e.g.,

CXXFLAGS=-g python test.py

Alternatively, we can set the flags from within a Python script

import dune.generator as generator
generator.addToFlags("-DWANT_CACHED_COMM_MANAGER=0",noChecks=True)
algorithm(...)
generator.setFlags("-g -Wfatal-errors",noChecks=True)
algorithm(...)
generator.reset()

Now one can use gdb to debug the C++ code

gdb python
(gdb) r test.py

Other available environment variables are

DUNE_LOG_LEVEL: set to info or debug to get more verbose output during module building/
DUNE_SAVE_BUILD: show full output from compiler during JIT compilation. Set to terminal to obtain output to console or set to write to obtain log files in current folder.
DUNE_PY_DIR: location of dune-py module
DUNE_CMAKE_FLAGS: cmake flags to use during configuration of a new dune-py module
DUNEPY_DISABLE_PLOTTING: disable plotting using the dune plotting functions