make FieldAdapter visible as before, to avoid breaking user code

nifty5/__init__.py

@@ -48,7 +48,7 @@ from .operators.block_diagonal_operator import BlockDiagonalOperator
 from .operators.outer_product_operator import OuterProduct
 from .operators.simple_linear_operators import (
     VdotOperator, ConjugationOperator, Realizer,
-    ducktape, GeometryRemover, NullOperator)
+    FieldAdapter, ducktape, GeometryRemover, NullOperator)
 from .operators.energy_operators import (
     EnergyOperator, GaussianEnergy, PoissonianEnergy, InverseGammaLikelihood,
     BernoulliEnergy, Hamiltonian, SampledKullbachLeiblerDivergence)

nifty5/operators/simple_linear_operators.py

@@ -62,7 +62,7 @@ class Realizer(EndomorphicOperator):
         return x.real
 
 
-class _FieldAdapter(LinearOperator):
+class FieldAdapter(LinearOperator):
     """Operator for conversion between Fields and MultiFields.
 
     Parameters
@@ -120,7 +120,7 @@ def ducktape(left, right, name):
             left = left.domain
         else:
             left = makeDomain(left)
-    return _FieldAdapter(left, name)
+    return FieldAdapter(left, name)
 
 
 class GeometryRemover(LinearOperator):