GroupBy Cleanup (pandas-dev#23971)

pandas/core/groupby/generic.py

@@ -826,8 +826,9 @@ def _aggregate_multiple_funcs(self, arg, _level):
         for name, func in arg:
             obj = self
             if name in results:
-                raise SpecificationError('Function names must be unique, '
-                                         'found multiple named %s' % name)
+                raise SpecificationError(
+                    'Function names must be unique, found multiple named '
+                    '{}'.format(name))
 
             # reset the cache so that we
             # only include the named selection
@@ -1027,8 +1028,7 @@ def nunique(self, dropna=True):
         try:
             sorter = np.lexsort((val, ids))
         except TypeError:  # catches object dtypes
-            msg = ('val.dtype must be object, got {dtype}'
-                   .format(dtype=val.dtype))
+            msg = 'val.dtype must be object, got {}'.format(val.dtype)
             assert val.dtype == object, msg
             val, _ = algorithms.factorize(val, sort=False)
             sorter = np.lexsort((val, ids))

pandas/core/groupby/groupby.py

@@ -1644,7 +1644,8 @@ def nth(self, n, dropna=None):
                 # just returns NaN
                 raise ValueError("For a DataFrame groupby, dropna must be "
                                  "either None, 'any' or 'all', "
-                                 "(was passed %s)." % (dropna),)
+                                 "(was passed {dropna}).".format(
+                                     dropna=dropna))
 
         # old behaviour, but with all and any support for DataFrames.
         # modified in GH 7559 to have better perf
@@ -2099,6 +2100,6 @@ def groupby(obj, by, **kwds):
         from pandas.core.groupby.generic import DataFrameGroupBy
         klass = DataFrameGroupBy
     else:  # pragma: no cover
-        raise TypeError('invalid type: %s' % type(obj))
+        raise TypeError('invalid type: {}'.format(obj))
 
     return klass(obj, by, **kwds)

pandas/core/groupby/grouper.py

@@ -257,7 +257,7 @@ def __init__(self, index, grouper=None, obj=None, name=None, level=None,
         if level is not None:
             if not isinstance(level, int):
                 if level not in index.names:
-                    raise AssertionError('Level %s not in index' % str(level))
+                    raise AssertionError('Level {} not in index'.format(level))
                 level = index.names.index(level)
 
             if self.name is None:
@@ -317,7 +317,8 @@ def __init__(self, index, grouper=None, obj=None, name=None, level=None,
                                 (Series, Index, ExtensionArray, np.ndarray)):
                 if getattr(self.grouper, 'ndim', 1) != 1:
                     t = self.name or str(type(self.grouper))
-                    raise ValueError("Grouper for '%s' not 1-dimensional" % t)
+                    raise ValueError(
+                        "Grouper for '{}' not 1-dimensional".format(t))
                 self.grouper = self.index.map(self.grouper)
                 if not (hasattr(self.grouper, "__len__") and
                         len(self.grouper) == len(self.index)):
@@ -460,8 +461,8 @@ def _get_grouper(obj, key=None, axis=0, level=None, sort=True,
 
             if isinstance(level, compat.string_types):
                 if obj.index.name != level:
-                    raise ValueError('level name %s is not the name of the '
-                                     'index' % level)
+                    raise ValueError('level name {} is not the name of the '
+                                     'index'.format(level))
             elif level > 0 or level < -1:
                 raise ValueError('level > 0 or level < -1 only valid with '
                                  ' MultiIndex')

pandas/core/groupby/ops.py

@@ -380,7 +380,8 @@ def get_func(fname):
 
             # otherwise find dtype-specific version, falling back to object
             for dt in [dtype_str, 'object']:
-                f = getattr(libgroupby, "%s_%s" % (fname, dtype_str), None)
+                f = getattr(libgroupby, "{fname}_{dtype_str}".format(
+                    fname=fname, dtype_str=dtype_str), None)
                 if f is not None:
                     return f
 
@@ -403,9 +404,11 @@ def wrapper(*args, **kwargs):
             func = get_func(ftype)
 
         if func is None:
-            raise NotImplementedError("function is not implemented for this"
-                                      "dtype: [how->%s,dtype->%s]" %
-                                      (how, dtype_str))
+            raise NotImplementedError(
+                "function is not implemented for this dtype: "
+                "[how->{how},dtype->{dtype_str}]".format(how=how,
+                                                         dtype_str=dtype_str))
+
         return func
 
     def _cython_operation(self, kind, values, how, axis, min_count=-1,
@@ -485,7 +488,8 @@ def _cython_operation(self, kind, values, how, axis, min_count=-1,
             out_dtype = 'float'
         else:
             if is_numeric:
-                out_dtype = '%s%d' % (values.dtype.kind, values.dtype.itemsize)
+                out_dtype = '{kind}{itemsize}'.format(
+                    kind=values.dtype.kind, itemsize=values.dtype.itemsize)
             else:
                 out_dtype = 'object'
 
@@ -739,10 +743,6 @@ def group_info(self):
                 obs_group_ids.astype('int64', copy=False),
                 ngroups)
 
-    @cache_readonly
-    def ngroups(self):
-        return len(self.result_index)
-
     @cache_readonly
     def result_index(self):
         if len(self.binlabels) != 0 and isna(self.binlabels[0]):
@@ -769,11 +769,6 @@ def agg_series(self, obj, func):
         grouper = reduction.SeriesBinGrouper(obj, func, self.bins, dummy)
         return grouper.get_result()
 
-    # ----------------------------------------------------------------------
-    # cython aggregation
-
-    _cython_functions = copy.deepcopy(BaseGrouper._cython_functions)
-
 
 def _get_axes(group):
     if isinstance(group, Series):
@@ -853,9 +848,6 @@ def _chop(self, sdata, slice_obj):
 
 class FrameSplitter(DataSplitter):
 
-    def __init__(self, data, labels, ngroups, axis=0):
-        super(FrameSplitter, self).__init__(data, labels, ngroups, axis=axis)
-
     def fast_apply(self, f, names):
         # must return keys::list, values::list, mutated::bool
         try: