How to use the petsc4py.PETSc.Viewer function in petsc4py

def test_ISRead(self):
        """Test reading an IS"""
        indices = np.array([3,4,5])
        anis = PETSc.IS().createGeneral(list(indices))
        viewer = PETSc.Viewer().createBinary('test.dat', PETSc.Viewer.Mode.W)
        anis.view(viewer)
        viewer.destroy()
        anis.destroy()

        result, = PetscBinaryIO().readBinaryFile('test.dat')
        self.assertTrue((indices == result).all())

def _petsc_view(obj, filename):
    """Saves object to disk using a PETSc binary viewer.
    """
    viewer = p4pyPETSc.Viewer().createBinary(filename, 'w')
    viewer(obj)
    viewer2 = p4pyPETSc.Viewer().createASCII(filename+".m", 'w')
    viewer2.setFormat(1)
    viewer2(obj)

def solve():
    opts = PETSc.Options()

    mat_filename = opts.getString('-mtx', 'mtx.dat')
    rhs_filename = opts.getString('-rhs', 'rhs.dat')
    sol0_filename = opts.getString('-sol0', '')
    sol_filename = opts.getString('-sol', 'sol.dat')
    status_filename = opts.getString('-status', 'status.txt')

    view_mtx = PETSc.Viewer().createBinary(mat_filename, mode='r')
    view_rhs = PETSc.Viewer().createBinary(rhs_filename, mode='r')

    mtx = PETSc.Mat().load(view_mtx)
    rhs = PETSc.Vec().load(view_rhs)

    ksp = PETSc.KSP().create()
    ksp.setOperators(mtx)
    ksp.setFromOptions()

    if not sol0_filename:
        sol = rhs.duplicate()

    else:
        view_sol0 = PETSc.Viewer().createBinary(sol0_filename, mode='r')
        sol = PETSc.Vec().load(view_sol0)
        ksp.setInitialGuessNonzero(True)

else:
        outDir = './'+_os.path.dirname(filename)

    # create output directory if it doesn't exist
    try:
        _os.mkdir(outDir)
    except OSError as exception:
        if exception.errno != _errno.EEXIST:
            raise

    vecArray = vecToArray(vec)
    matArray = vecArray.reshape([_np.sqrt(vecArray.size),_np.sqrt(vecArray.size)])

    if filetype == 'txt':
        #if rank == 0:  _np.savetxt(filename,matArray)
        txtSave = _PETSc.Viewer().createASCII(filename, 'w',
            format=_PETSc.Viewer.Format.ASCII_DENSE, comm=_PETSc.COMM_WORLD)
        txtSave(arrayToMat(matArray))
        txtSave.destroy()

        if rank == 0:
            for line in _fl.FileInput(filename,inplace=1):
                if line[2] != 't':
                    line = line.replace(" i","j")
                    line = line.replace(" -","-")
                    line = line.replace("+-","-")
                    print line,

    elif filetype == 'bin':
        binSave = _PETSc.Viewer().createBinary(filename, 'w', comm=_PETSc.COMM_WORLD)
        binSave(arrayToMat(matArray))
        binSave.destroy()

#if rank == 0:  _np.savetxt(filename,matArray)
        txtSave = _PETSc.Viewer().createASCII(filename, 'w',
            format=_PETSc.Viewer.Format.ASCII_DENSE, comm=_PETSc.COMM_WORLD)
        txtSave(arrayToMat(matArray))
        txtSave.destroy()

        if rank == 0:
            for line in _fl.FileInput(filename,inplace=1):
                if line[2] != 't':
                    line = line.replace(" i","j")
                    line = line.replace(" -","-")
                    line = line.replace("+-","-")
                    print line,

    elif filetype == 'bin':
        binSave = _PETSc.Viewer().createBinary(filename, 'w', comm=_PETSc.COMM_WORLD)
        binSave(arrayToMat(matArray))
        binSave.destroy()
    vec.comm.barrier()

t0 = 0.0
    Tend = 1.0

    # instantiate controller
    controller = controller_nonMPI(num_procs=1, controller_params=controller_params, description=description)

    # get initial values on finest level
    P = controller.MS[0].levels[0].prob
    uinit = P.u_exact(t0)

    # call main function to get things done...
    uend, stats = controller.run(u0=uinit, t0=t0, Tend=Tend)

    # load reference solution to compare with
    fname = cwd + 'data/GS_reference.dat'
    viewer = PETSc.Viewer().createBinary(fname, 'r')
    uex = P.u_exact(t0)
    uex.values = PETSc.Vec().load(viewer)
    err = abs(uex - uend)

    # filter statistics by variant (number of iterations)
    filtered_stats = filter_stats(stats, type='niter')

    # convert filtered statistics to list of iterations count, sorted by process
    iter_counts = sort_stats(filtered_stats, sortby='time')

    # compute and print statistics
    niters = np.array([item[1] for item in iter_counts])
    out = '   Mean number of iterations: %4.2f' % np.mean(niters)
    print(out)
    out = '   Range of values for number of iterations: %2i ' % np.ptp(niters)
    print(out)

def _petsc_view(obj, filename):
    """Saves petsc object to disk using a PETSc binary viewer.

    Parameters
    ----------
    obj : PETSc obj
        PETSc4py object to be saved (e.g. vector, matrix, etc)
    filename : str
        String with PETSc filename
    """
    viewer = p4pyPETSc.Viewer().createBinary(filename, 'w')
    viewer(obj)
    viewer2 = p4pyPETSc.Viewer().createASCII(filename+".m", 'w')
    viewer2.pushFormat(1)
    viewer2(obj)
    viewer2.popFormat()

def _vector_load(directory, filename, mpi_comm):
        if _file_exists(directory, filename + ".dat", mpi_comm):
            viewer = PETSc.Viewer().createBinary(os.path.join(str(directory), filename + ".dat"), "r", mpi_comm)
            return PETSc.Vec().load(viewer)
        else:
            raise OSError

rank = _PETSc.Comm.Get_rank(_PETSc.COMM_WORLD)

    if _os.path.isabs(filename):
        outDir = _os.path.dirname(filename)
    else:
        outDir = './'+_os.path.dirname(filename)

    # create output directory if it doesn't exist
    try:
        _os.mkdir(outDir)
    except OSError as exception:
        if exception.errno != _errno.EEXIST:
            raise

    if filetype == 'txt':
        txtSave = _PETSc.Viewer().createASCII(filename, 'w',
            format=_PETSc.Viewer.Format.ASCII_DENSE, comm=_PETSc.COMM_WORLD)
        txtSave(mat)
        txtSave.destroy()

        if rank == 0:
            for line in _fl.FileInput(filename,inplace=1):
                if line[2] != 't':
                    if mattype == 'adj':
                        line = line.replace(" i","j")
                        line = line.replace(" -","-")
                        line = line.replace("+-","-")
                        line = line.replace("0000e+01+0.00000e+00j","")
                        line = line.replace(".00000e+00+0.00000e+00j","")
                        line = line.replace(".","")
                        line = line.replace(" -","\t-")
                        line = line.replace("  ","\t")

out = '   Position of max/min number of iterations: %2i -- %2i' % \
          (int(np.argmax(niters)), int(np.argmin(niters)))
    print(out)
    out = '   Std and var for number of iterations: %4.2f -- %4.2f' % (float(np.std(niters)), float(np.var(niters)))
    print(out)

    print('Iteration count (nonlinear/linear): %i / %i' % (P.snes_itercount, P.ksp_itercount))
    print('Mean Iteration count per call: %4.2f / %4.2f' % (P.snes_itercount / max(P.snes_ncalls, 1),
                                                            P.ksp_itercount / max(P.ksp_ncalls, 1)))

    timing = sort_stats(filter_stats(stats, type='timing_run'), sortby='time')

    print('Time to solution: %6.4f sec.' % timing[0][1])

    fname = 'data/GS_reference.dat'
    viewer = PETSc.Viewer().createBinary(fname, 'w')
    viewer.view(uend.values)

    assert os.path.isfile(fname), 'ERROR: PETSc did not create file'

    return None