diff --git a/nifty5/operators/block_diagonal_operator.py b/nifty5/operators/block_diagonal_operator.py
index 2006ff11655841000c195b55f07783076d45389d..7320215504d48805a5e78ca9626ef4e45f0a829a 100644
--- a/nifty5/operators/block_diagonal_operator.py
+++ b/nifty5/operators/block_diagonal_operator.py
@@ -19,9 +19,9 @@
 from __future__ import absolute_import, division, print_function
 
 from ..compat import *
-from .endomorphic_operator import EndomorphicOperator
 from ..multi_domain import MultiDomain
 from ..multi_field import MultiField
+from .endomorphic_operator import EndomorphicOperator
 
 
 class BlockDiagonalOperator(EndomorphicOperator):
diff --git a/nifty5/operators/central_zero_padder.py b/nifty5/operators/central_zero_padder.py
index 414cab51cc7fede5ea574cd8a7d0030248476b5d..36e303822c2c99f90edc2101b95c2d477d49ea4d 100644
--- a/nifty5/operators/central_zero_padder.py
+++ b/nifty5/operators/central_zero_padder.py
@@ -18,16 +18,16 @@
 
 from __future__ import absolute_import, division, print_function
 
-import numpy as np
 import itertools
 
+import numpy as np
+
+from .. import dobj, utilities
 from ..compat import *
-from .. import utilities
-from .linear_operator import LinearOperator
 from ..domain_tuple import DomainTuple
 from ..domains.rg_space import RGSpace
 from ..field import Field
-from .. import dobj
+from .linear_operator import LinearOperator
 
 
 # MR FIXME: for even axis lengths, we probably should split the value at the
@@ -95,7 +95,6 @@ class CentralZeroPadder(LinearOperator):
         self._check_input(x, mode)
         x = x.val
         dax = dobj.distaxis(x)
-        shp_in = x.shape
         shp_out = self._tgt(mode).shape
         axes = self._target.axes[self._space]
         if dax in axes:
diff --git a/nifty5/operators/chain_operator.py b/nifty5/operators/chain_operator.py
index 5e8025e5b6c72d9a38ba45f4baa6cc18bbd4f6c5..b25d8bc07d80cf8e10f8b7134b7e2db8e8f5261a 100644
--- a/nifty5/operators/chain_operator.py
+++ b/nifty5/operators/chain_operator.py
@@ -18,13 +18,11 @@
 
 from __future__ import absolute_import, division, print_function
 
-import numpy as np
-
+from .. import utilities
 from ..compat import *
+from .diagonal_operator import DiagonalOperator
 from .linear_operator import LinearOperator
-from .. import utilities
 from .scaling_operator import ScalingOperator
-from .diagonal_operator import DiagonalOperator
 from .simple_linear_operators import NullOperator
 
 
@@ -44,8 +42,8 @@ class ChainOperator(LinearOperator):
     @staticmethod
     def simplify(ops):
         # verify domains
-        for i in range(len(ops)-1):
-            if ops[i+1].target != ops[i].domain:
+        for i in range(len(ops) - 1):
+            if ops[i + 1].target != ops[i].domain:
                 raise ValueError("domain mismatch")
         # unpack ChainOperators
         opsnew = []
@@ -78,9 +76,8 @@ class ChainOperator(LinearOperator):
         # combine DiagonalOperators where possible
         opsnew = []
         for op in ops:
-            if (len(opsnew) > 0 and
-                    isinstance(opsnew[-1], DiagonalOperator) and
-                    isinstance(op, DiagonalOperator)):
+            if (len(opsnew) > 0 and isinstance(opsnew[-1], DiagonalOperator)
+                    and isinstance(op, DiagonalOperator)):
                 opsnew[-1] = opsnew[-1]._combine_prod(op)
             else:
                 opsnew.append(op)
@@ -89,9 +86,9 @@ class ChainOperator(LinearOperator):
         from .block_diagonal_operator import BlockDiagonalOperator
         opsnew = []
         for op in ops:
-            if (len(opsnew) > 0 and
-                    isinstance(opsnew[-1], BlockDiagonalOperator) and
-                    isinstance(op, BlockDiagonalOperator)):
+            if (len(opsnew) > 0
+                    and isinstance(opsnew[-1], BlockDiagonalOperator)
+                    and isinstance(op, BlockDiagonalOperator)):
                 opsnew[-1] = opsnew[-1]._combine_chain(op)
             else:
                 opsnew.append(op)
@@ -123,8 +120,8 @@ class ChainOperator(LinearOperator):
         if trafo == 0:
             return self
         if trafo == ADJ or trafo == INV:
-            return self.make([op._flip_modes(trafo)
-                              for op in reversed(self._ops)])
+            return self.make(
+                [op._flip_modes(trafo) for op in reversed(self._ops)])
         if trafo == ADJ | INV:
             return self.make([op._flip_modes(trafo) for op in self._ops])
         raise ValueError("invalid operator transformation")
@@ -136,6 +133,7 @@ class ChainOperator(LinearOperator):
             x = op.apply(x, mode)
         return x
 
+
 #     def draw_sample(self, from_inverse=False, dtype=np.float64):
 #         from ..sugar import from_random
 #         if len(self._ops) == 1:
@@ -149,4 +147,4 @@ class ChainOperator(LinearOperator):
 
     def __repr__(self):
         subs = "\n".join(sub.__repr__() for sub in self._ops)
-        return "ChainOperator:\n"+utilities.indent(subs)
+        return "ChainOperator:\n" + utilities.indent(subs)
diff --git a/nifty5/operators/domain_distributor.py b/nifty5/operators/domain_distributor.py
index 6044e6e32161f1eb24fefddd8aa4cf5d20d1d15e..da744a1026fbd1698e5ab1dcdab3100cfab33f34 100644
--- a/nifty5/operators/domain_distributor.py
+++ b/nifty5/operators/domain_distributor.py
@@ -20,12 +20,11 @@ from __future__ import absolute_import, division, print_function
 
 import numpy as np
 
-from .. import dobj
+from .. import utilities
 from ..compat import *
 from ..domain_tuple import DomainTuple
 from ..field import Field
 from .linear_operator import LinearOperator
-from .. import utilities
 
 
 class DomainDistributor(LinearOperator):
diff --git a/nifty5/operators/energy_operators.py b/nifty5/operators/energy_operators.py
index e0e3ce674434a7a9b758aa84412436c5708d9ddb..7d502421e295b5f3f79697b9cf187ac202e56440 100644
--- a/nifty5/operators/energy_operators.py
+++ b/nifty5/operators/energy_operators.py
@@ -18,15 +18,15 @@
 
 from __future__ import absolute_import, division, print_function
 
+from .. import utilities
 from ..compat import *
 from ..domain_tuple import DomainTuple
+from ..field import Field
+from ..linearization import Linearization
+from ..sugar import makeOp
 from .operator import Operator
-from .sandwich_operator import SandwichOperator
 from .sampling_enabler import SamplingEnabler
-from ..sugar import makeOp
-from ..linearization import Linearization
-from .. import utilities
-from ..field import Field
+from .sandwich_operator import SandwichOperator
 from .simple_linear_operators import VdotOperator
 
 
diff --git a/nifty5/operators/exp_transform.py b/nifty5/operators/exp_transform.py
index b27505bc54d2fc9a7534c95aa8a50a0f0b2c31c2..252830adb8a2604faf0bea446ded68e8427a5e6e 100644
--- a/nifty5/operators/exp_transform.py
+++ b/nifty5/operators/exp_transform.py
@@ -26,8 +26,8 @@ from ..domain_tuple import DomainTuple
 from ..domains.power_space import PowerSpace
 from ..domains.rg_space import RGSpace
 from ..field import Field
-from .linear_operator import LinearOperator
 from ..utilities import infer_space, special_add_at
+from .linear_operator import LinearOperator
 
 
 class ExpTransform(LinearOperator):
diff --git a/nifty5/operators/field_zero_padder.py b/nifty5/operators/field_zero_padder.py
index 60be737c4b882b289f6f472a3a6b938b2d8a6699..f39cb28ae981e59a07fbdae78ea80e0b537738a4 100644
--- a/nifty5/operators/field_zero_padder.py
+++ b/nifty5/operators/field_zero_padder.py
@@ -2,13 +2,12 @@ from __future__ import absolute_import, division, print_function
 
 import numpy as np
 
-from .. import dobj
+from .. import dobj, utilities
 from ..compat import *
 from ..domain_tuple import DomainTuple
 from ..domains.rg_space import RGSpace
 from ..field import Field
 from .linear_operator import LinearOperator
-from .. import utilities
 
 
 class FieldZeroPadder(LinearOperator):
diff --git a/nifty5/operators/harmonic_operators.py b/nifty5/operators/harmonic_operators.py
index 480540848da3eb06ee8fd0dfd8ed976705c71ba9..4ac2a595270ae1254c4bb00e2939b9c558be2c20 100644
--- a/nifty5/operators/harmonic_operators.py
+++ b/nifty5/operators/harmonic_operators.py
@@ -23,12 +23,12 @@ import numpy as np
 from .. import dobj, utilities
 from ..compat import *
 from ..domain_tuple import DomainTuple
-from ..domains.rg_space import RGSpace
-from ..domains.lm_space import LMSpace
 from ..domains.gl_space import GLSpace
+from ..domains.lm_space import LMSpace
+from ..domains.rg_space import RGSpace
 from ..field import Field
-from .linear_operator import LinearOperator
 from .diagonal_operator import DiagonalOperator
+from .linear_operator import LinearOperator
 from .scaling_operator import ScalingOperator
 
 
diff --git a/nifty5/operators/linear_operator.py b/nifty5/operators/linear_operator.py
index d2000e99788d047bb2ecbcc728c425e68de94218..26a0cf81dc0dfac484ce06f2ba567158198c09c6 100644
--- a/nifty5/operators/linear_operator.py
+++ b/nifty5/operators/linear_operator.py
@@ -18,8 +18,6 @@
 
 from __future__ import absolute_import, division, print_function
 
-import numpy as np
-
 from ..compat import *
 from .operator import Operator
 
diff --git a/nifty5/operators/operator.py b/nifty5/operators/operator.py
index e3a8e815bfcfea248dfc6a896f4241e81cc389a0..73ece15e64ef3e1f64b8d8e27f75e09f4ced4f89 100644
--- a/nifty5/operators/operator.py
+++ b/nifty5/operators/operator.py
@@ -1,8 +1,7 @@
 from __future__ import absolute_import, division, print_function
 
 from ..compat import *
-from ..utilities import NiftyMetaBase, my_product
-from ..domain_tuple import DomainTuple
+from ..utilities import NiftyMetaBase
 
 
 class Operator(NiftyMetaBase()):
diff --git a/nifty5/operators/scaling_operator.py b/nifty5/operators/scaling_operator.py
index 051a4f30f7f79d4c5ed76bad34cee6262eb7e251..dac7bdb2a244c96cb218a6506bc7af2e0b1b01fe 100644
--- a/nifty5/operators/scaling_operator.py
+++ b/nifty5/operators/scaling_operator.py
@@ -21,10 +21,8 @@ from __future__ import absolute_import, division, print_function
 import numpy as np
 
 from ..compat import *
-from ..domain_tuple import DomainTuple
 from ..sugar import full
 from .endomorphic_operator import EndomorphicOperator
-from .. import utilities
 
 
 class ScalingOperator(EndomorphicOperator):
diff --git a/nifty5/operators/simple_linear_operators.py b/nifty5/operators/simple_linear_operators.py
index 05d5f640afa301be1b0d36db6c2ef40a32ac6b1f..e011778ef14089caaabcf2e2ba9753fb7d2049bf 100644
--- a/nifty5/operators/simple_linear_operators.py
+++ b/nifty5/operators/simple_linear_operators.py
@@ -18,17 +18,15 @@
 
 from __future__ import absolute_import, division, print_function
 
-import numpy as np
-
 from ..compat import *
 from ..domain_tuple import DomainTuple
-from ..multi_domain import MultiDomain
 from ..domains.unstructured_domain import UnstructuredDomain
-from .linear_operator import LinearOperator
-from .endomorphic_operator import EndomorphicOperator
-from ..sugar import full
 from ..field import Field
+from ..multi_domain import MultiDomain
 from ..multi_field import MultiField
+from ..sugar import full
+from .endomorphic_operator import EndomorphicOperator
+from .linear_operator import LinearOperator
 
 
 class VdotOperator(LinearOperator):
diff --git a/nifty5/operators/sum_operator.py b/nifty5/operators/sum_operator.py
index 0b46a0b487d57b93cf0d2e0a1aa3b71ca3ab6443..97806be7207550f369b8bf3fd8749f313d02451a 100644
--- a/nifty5/operators/sum_operator.py
+++ b/nifty5/operators/sum_operator.py
@@ -18,16 +18,15 @@
 
 from __future__ import absolute_import, division, print_function
 
+from collections import defaultdict
+
 import numpy as np
 
 from ..compat import *
-from ..utilities import my_sum, indent
-from .linear_operator import LinearOperator
-from .scaling_operator import ScalingOperator
-from .diagonal_operator import DiagonalOperator
-from .block_diagonal_operator import BlockDiagonalOperator
-from collections import defaultdict
 from ..sugar import domain_union
+from ..utilities import indent
+from .block_diagonal_operator import BlockDiagonalOperator
+from .linear_operator import LinearOperator
 
 
 class SumOperator(LinearOperator):
diff --git a/nifty5/operators/symmetrizing_operator.py b/nifty5/operators/symmetrizing_operator.py
index 0681e3dffc83289e74a3ed996552568ed7497718..09a5b9b893a67b118af9053df1823363a9d5a12a 100644
--- a/nifty5/operators/symmetrizing_operator.py
+++ b/nifty5/operators/symmetrizing_operator.py
@@ -18,13 +18,12 @@
 
 from __future__ import absolute_import, division, print_function
 
-from .. import dobj
+from .. import dobj, utilities
 from ..compat import *
 from ..domain_tuple import DomainTuple
 from ..domains.log_rg_space import LogRGSpace
 from ..field import Field
 from .endomorphic_operator import EndomorphicOperator
-from .. import utilities
 
 
 class SymmetrizingOperator(EndomorphicOperator):