diff --git a/pandas/core/groupby/base.py b/pandas/core/groupby/base.py
index ac84971de08d8..9ef30b8fd021f 100644
--- a/pandas/core/groupby/base.py
+++ b/pandas/core/groupby/base.py
@@ -5,8 +5,9 @@
 """
 
 import types
+
+from pandas.core.dtypes.common import is_list_like, is_scalar
 from pandas.util._decorators import make_signature
-from pandas.core.dtypes.common import is_scalar, is_list_like
 
 
 class GroupByMixin(object):
diff --git a/pandas/core/groupby/categorical.py b/pandas/core/groupby/categorical.py
index e54045884ea93..3e653704bbace 100644
--- a/pandas/core/groupby/categorical.py
+++ b/pandas/core/groupby/categorical.py
@@ -1,7 +1,9 @@
 import numpy as np
+
 from pandas.core.algorithms import unique1d
 from pandas.core.arrays.categorical import (
-    _recode_for_categories, CategoricalDtype, Categorical)
+    Categorical, CategoricalDtype, _recode_for_categories
+)
 
 
 def recode_for_groupby(c, sort, observed):
diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 63bf67854e5cd..a832eecf87721 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -7,48 +7,40 @@
 """
 
 import collections
-import warnings
 import copy
-from textwrap import dedent
+import warnings
 from functools import partial
+from textwrap import dedent
 
 import numpy as np
 
-from pandas._libs import lib, Timestamp
-from pandas.util._decorators import Substitution, Appender
-from pandas import compat
-
-import pandas.core.indexes.base as ibase
+import pandas.core.algorithms as algorithms
 import pandas.core.common as com
-from pandas.core.panel import Panel
+import pandas.core.indexes.base as ibase
+from pandas import compat
+from pandas._libs import Timestamp, lib
 from pandas.compat import lzip, map
-
-from pandas.core.series import Series
-from pandas.core.generic import _shared_docs
-from pandas.core.groupby.groupby import (
-    GroupBy, _apply_docs, _transform_template)
-from pandas.core.generic import NDFrame
-from pandas.core.groupby import base
+from pandas.compat.numpy import _np_version_under1p13
+from pandas.core.arrays import Categorical
+from pandas.core.base import DataError, SpecificationError
+from pandas.core.dtypes.cast import maybe_downcast_to_dtype
 from pandas.core.dtypes.common import (
-    is_scalar,
-    is_bool,
-    is_datetimelike,
-    is_numeric_dtype,
-    is_integer_dtype,
-    is_interval_dtype,
-    ensure_platform_int,
-    ensure_int64)
+    ensure_int64, ensure_platform_int, is_bool, is_datetimelike,
+    is_integer_dtype, is_interval_dtype, is_numeric_dtype, is_scalar
+)
 from pandas.core.dtypes.missing import isna, notna
-import pandas.core.algorithms as algorithms
 from pandas.core.frame import DataFrame
-from pandas.core.dtypes.cast import maybe_downcast_to_dtype
-from pandas.core.base import SpecificationError, DataError
-from pandas.core.index import Index, MultiIndex, CategoricalIndex
-from pandas.core.arrays import Categorical
+from pandas.core.generic import NDFrame, _shared_docs
+from pandas.core.groupby import base
+from pandas.core.groupby.groupby import (
+    GroupBy, _apply_docs, _transform_template
+)
+from pandas.core.index import CategoricalIndex, Index, MultiIndex
 from pandas.core.internals import BlockManager, make_block
-from pandas.compat.numpy import _np_version_under1p13
-
+from pandas.core.panel import Panel
+from pandas.core.series import Series
 from pandas.plotting._core import boxplot_frame_groupby
+from pandas.util._decorators import Appender, Substitution
 
 
 class NDFrameGroupBy(GroupBy):
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 025be781d9ee8..5acccbf688e30 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -7,42 +7,36 @@ class providing the base-class of operations.
 expose these user-facing objects to provide specific functionailty.
 """
 
-import types
-from functools import wraps, partial
-import datetime
 import collections
+import datetime
+import types
 import warnings
 from contextlib import contextmanager
+from functools import partial, wraps
 
 import numpy as np
 
-from pandas._libs import groupby as libgroupby, Timestamp
-from pandas.util._validators import validate_kwargs
-from pandas.util._decorators import (
-    cache_readonly, Substitution, Appender)
-
+import pandas.core.algorithms as algorithms
+import pandas.core.common as com
 from pandas import compat
-from pandas.compat import zip, range, callable, set_function_name
+from pandas._libs import Timestamp, groupby as libgroupby
+from pandas.compat import callable, range, set_function_name, zip
 from pandas.compat.numpy import function as nv
-
-from pandas.core.dtypes.common import (
-    is_numeric_dtype,
-    is_scalar,
-    ensure_float)
+from pandas.core.base import (
+    DataError, GroupByError, PandasObject, SelectionMixin, SpecificationError
+)
+from pandas.core.config import option_context
 from pandas.core.dtypes.cast import maybe_downcast_to_dtype
+from pandas.core.dtypes.common import ensure_float, is_numeric_dtype, is_scalar
 from pandas.core.dtypes.missing import isna, notna
-
+from pandas.core.frame import DataFrame
+from pandas.core.generic import NDFrame
 from pandas.core.groupby import base
-from pandas.core.base import (PandasObject, SelectionMixin, GroupByError,
-                              DataError, SpecificationError)
 from pandas.core.index import Index, MultiIndex
-from pandas.core.generic import NDFrame
-from pandas.core.frame import DataFrame
 from pandas.core.series import Series
 from pandas.core.sorting import get_group_index_sorter
-import pandas.core.common as com
-import pandas.core.algorithms as algorithms
-from pandas.core.config import option_context
+from pandas.util._decorators import Appender, Substitution, cache_readonly
+from pandas.util._validators import validate_kwargs
 
 _doc_template = """
 
diff --git a/pandas/core/groupby/grouper.py b/pandas/core/groupby/grouper.py
index 1c8fe0e6cadad..cbe87040b8117 100644
--- a/pandas/core/groupby/grouper.py
+++ b/pandas/core/groupby/grouper.py
@@ -4,31 +4,25 @@
 """
 
 import warnings
-import numpy as np
 
-from pandas.util._decorators import cache_readonly
+import numpy as np
 
+import pandas.core.algorithms as algorithms
+import pandas.core.common as com
 from pandas import compat
-from pandas.compat import zip, callable
-
-from pandas.core.dtypes.generic import ABCSeries
-from pandas.core.arrays import ExtensionArray, Categorical
-from pandas.core.index import (
-    Index, MultiIndex, CategoricalIndex)
+from pandas.compat import callable, zip
+from pandas.core.arrays import Categorical, ExtensionArray
 from pandas.core.dtypes.common import (
-    ensure_categorical,
-    is_hashable,
-    is_list_like,
-    is_timedelta64_dtype,
-    is_datetime64_dtype,
-    is_categorical_dtype,
-    is_scalar)
-from pandas.core.series import Series
+    ensure_categorical, is_categorical_dtype, is_datetime64_dtype, is_hashable,
+    is_list_like, is_scalar, is_timedelta64_dtype
+)
+from pandas.core.dtypes.generic import ABCSeries
 from pandas.core.frame import DataFrame
-import pandas.core.common as com
 from pandas.core.groupby.ops import BaseGrouper
-import pandas.core.algorithms as algorithms
+from pandas.core.index import CategoricalIndex, Index, MultiIndex
+from pandas.core.series import Series
 from pandas.io.formats.printing import pprint_thing
+from pandas.util._decorators import cache_readonly
 
 
 class Grouper(object):
diff --git a/pandas/core/groupby/ops.py b/pandas/core/groupby/ops.py
index b199127ac867b..af22744c4feec 100644
--- a/pandas/core/groupby/ops.py
+++ b/pandas/core/groupby/ops.py
@@ -6,42 +6,33 @@
 are contained *in* the SeriesGroupBy and DataFrameGroupBy objects.
 """
 
-import copy
 import collections
-import numpy as np
-
-from pandas._libs import lib, reduction, NaT, iNaT, groupby as libgroupby
-from pandas.util._decorators import cache_readonly
+import copy
 
-from pandas.compat import zip, range, lzip
+import numpy as np
 
+import pandas.core.algorithms as algorithms
+import pandas.core.common as com
+from pandas._libs import NaT, groupby as libgroupby, iNaT, lib, reduction
+from pandas.compat import lzip, range, zip
 from pandas.core.base import SelectionMixin
-from pandas.core.dtypes.missing import isna, _maybe_fill
-from pandas.core.index import (
-    Index, MultiIndex, ensure_index)
 from pandas.core.dtypes.common import (
-    ensure_float64,
-    ensure_platform_int,
-    ensure_int64,
-    ensure_int64_or_float64,
-    ensure_object,
-    needs_i8_conversion,
-    is_integer_dtype,
-    is_complex_dtype,
-    is_bool_dtype,
-    is_numeric_dtype,
-    is_timedelta64_dtype,
-    is_datetime64_any_dtype,
-    is_categorical_dtype)
-from pandas.core.series import Series
+    ensure_float64, ensure_int64, ensure_int64_or_float64, ensure_object,
+    ensure_platform_int, is_bool_dtype, is_categorical_dtype, is_complex_dtype,
+    is_datetime64_any_dtype, is_integer_dtype, is_numeric_dtype,
+    is_timedelta64_dtype, needs_i8_conversion
+)
+from pandas.core.dtypes.missing import _maybe_fill, isna
 from pandas.core.frame import DataFrame
 from pandas.core.generic import NDFrame
-import pandas.core.common as com
 from pandas.core.groupby import base
-from pandas.core.sorting import (get_group_index_sorter, get_group_index,
-                                 compress_group_index, get_flattened_iterator,
-                                 decons_obs_group_ids, get_indexer_dict)
-import pandas.core.algorithms as algorithms
+from pandas.core.index import Index, MultiIndex, ensure_index
+from pandas.core.series import Series
+from pandas.core.sorting import (
+    compress_group_index, decons_obs_group_ids, get_flattened_iterator,
+    get_group_index, get_group_index_sorter, get_indexer_dict
+)
+from pandas.util._decorators import cache_readonly
 
 
 def generate_bins_generic(values, binner, closed):
diff --git a/setup.cfg b/setup.cfg
index ee39844996025..9eee370dc9f1f 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -182,12 +182,6 @@ skip=
     pandas/core/internals/concat.py,
     pandas/core/internals/managers.py,
     pandas/core/internals/blocks.py,
-    pandas/core/groupby/ops.py,
-    pandas/core/groupby/categorical.py,
-    pandas/core/groupby/generic.py,
-    pandas/core/groupby/groupby.py,
-    pandas/core/groupby/grouper.py,
-    pandas/core/groupby/base.py,
     pandas/core/reshape/concat.py,
     pandas/core/reshape/tile.py,
     pandas/core/reshape/melt.py,