diff --git a/nifty/field_types/field_array.py b/nifty/field_types/field_array.py
index bac80ea37fdd739c167058ef2102460d9457c230..4318afa2f3b029c246d992bdaf1cfc25358c8600 100644
--- a/nifty/field_types/field_array.py
+++ b/nifty/field_types/field_array.py
@@ -22,12 +22,11 @@ from field_type import FieldType
 class FieldArray(FieldType):
 
     def __init__(self, shape):
+        super(FieldArray, self).__init__()
         try:
-            new_shape = tuple([int(i) for i in shape])
+            self._shape = tuple([int(i) for i in shape])
         except TypeError:
-            new_shape = (int(shape), )
-        self._shape = new_shape
-        super(FieldArray, self).__init__()
+            self._shape = (int(shape), )
 
     @property
     def shape(self):
diff --git a/nifty/operators/invertible_operator_mixin/invertible_operator_mixin.py b/nifty/operators/invertible_operator_mixin/invertible_operator_mixin.py
index 4786a4f9375c7e56e6b52d38005263f2b6f69057..5aaff1097cf10aeeee14ca7232067ed783ff85cc 100644
--- a/nifty/operators/invertible_operator_mixin/invertible_operator_mixin.py
+++ b/nifty/operators/invertible_operator_mixin/invertible_operator_mixin.py
@@ -104,6 +104,7 @@ class InvertibleOperatorMixin(object):
                                                 x0=x0)
         return result
 
+    #MR FIXME: why? shouldn't this be equivalent to the adjoint inverse?
     def _inverse_adjoint_times(self, x, spaces):
         raise NotImplementedError(
             "no generic instance method 'inverse_adjoint_times'.")
diff --git a/nifty/operators/propagator_operator/harmonic_propagator_operator.py b/nifty/operators/propagator_operator/harmonic_propagator_operator.py
index 908e2e372f992dbd0c7afc7ce8fdbc0c62c94833..8789847a8a96dbc2dfa679cf388c5e213fdd6636 100644
--- a/nifty/operators/propagator_operator/harmonic_propagator_operator.py
+++ b/nifty/operators/propagator_operator/harmonic_propagator_operator.py
@@ -83,7 +83,7 @@ class HarmonicPropagatorOperator(InvertibleOperatorMixin, EndomorphicOperator):
 
     # ---Overwritten properties and methods---
 
-    def __init__(self, S=None, M=None, R=None, N=None, inverter=None,
+    def __init__(self, S, M=None, R=None, N=None, inverter=None,
                  preconditioner=None):
         """
             Sets the standard operator properties and `codomain`, `_A1`, `_A2`,
@@ -102,7 +102,6 @@ class HarmonicPropagatorOperator(InvertibleOperatorMixin, EndomorphicOperator):
 
         """
         # infer domain, and target
-        # infer domain, and target
         if M is not None:
             self._codomain = M.domain
             self._likelihood = M.times
diff --git a/nifty/spaces/power_space/power_space.py b/nifty/spaces/power_space/power_space.py
index ce56812a48db1ddc2751f60dbdd1f60cb101e77c..1e3fbcccff9f9a98d4339fbb7327dcc555a5ce1d 100644
--- a/nifty/spaces/power_space/power_space.py
+++ b/nifty/spaces/power_space/power_space.py
@@ -261,6 +261,7 @@ class PowerSpace(Space):
         hdf5_group.attrs['nbin'] = str(self.config["nbin"])
         hdf5_group.attrs['binbounds'] = str(self.config["binbounds"])
 
+        #MR FIXME: why not "return None" as happens everywhere else?
         return {
             'harmonic_partner': self.harmonic_partner,
             'pindex': self.pindex,
diff --git a/nifty/spaces/space/space.py b/nifty/spaces/space/space.py
index 84314c48cc968c41d94320d26ee0ba9c4f615d3d..624207d9c44e25800c95e8b90ee0c3e9c54a330f 100644
--- a/nifty/spaces/space/space.py
+++ b/nifty/spaces/space/space.py
@@ -202,6 +202,4 @@ class Space(DomainObject):
         raise NotImplementedError
 
     def __repr__(self):
-        string = ""
-        string += str(type(self)) + "\n"
-        return string
+        return str(type(self)) + "\n"
diff --git a/nifty/sugar.py b/nifty/sugar.py
index 5bf7dbc6f8b23f2753bebe1cde110462549dfcbb..11aa25bc76948de2c8f2757cf28a66399c0cc79e 100644
--- a/nifty/sugar.py
+++ b/nifty/sugar.py
@@ -18,27 +18,18 @@
 
 from nifty import PowerSpace,\
                   Field,\
-                  DiagonalOperator,\
-                  FFTOperator
+                  DiagonalOperator
 
 __all__ = ['create_power_operator']
 
 
 def create_power_operator(domain, power_spectrum, dtype=None,
                           distribution_strategy='not'):
-    if not domain.harmonic:
-        fft = FFTOperator(domain)
-        domain = fft.target[0]
 
     power_domain = PowerSpace(domain,
                               distribution_strategy=distribution_strategy)
-
-    fp = Field(power_domain,
-               val=power_spectrum, dtype=dtype,
+    fp = Field(power_domain, val=power_spectrum, dtype=dtype,
                distribution_strategy=distribution_strategy)
-
     f = fp.power_synthesize(mean=1, std=0, real_signal=False)
 
-    power_operator = DiagonalOperator(domain, diagonal=f, bare=True)
-
-    return power_operator
\ No newline at end of file
+    return DiagonalOperator(domain, diagonal=f, bare=True)