REF: make FrameApply less stateful, no self.results

pandas/core/apply.py

@@ -1,6 +1,6 @@
 import abc
 import inspect
-from typing import TYPE_CHECKING, Iterator, Type
+from typing import TYPE_CHECKING, Any, Dict, Iterator, Optional, Type, Union
 
 import numpy as np
 
@@ -18,6 +18,8 @@
 if TYPE_CHECKING:
     from pandas import DataFrame, Series, Index
 
+ResType = Dict[int, Any]
+
 
 def frame_apply(
     obj: "DataFrame",
@@ -64,10 +66,15 @@ def result_index(self) -> "Index":
     def result_columns(self) -> "Index":
         pass
 
+    @property
     @abc.abstractmethod
     def series_generator(self) -> Iterator["Series"]:
         pass
 
+    @abc.abstractmethod
+    def wrap_results_for_axis(self, results: ResType) -> Union["Series", "DataFrame"]:
+        pass
+
     # ---------------------------------------------------------------
 
     def __init__(
@@ -107,8 +114,16 @@ def f(x):
 
         # results
         self.result = None
-        self.res_index = None
-        self.res_columns = None
+        self._res_index: Optional["Index"] = None
+
+    @property
+    def res_index(self) -> "Index":
+        assert self._res_index is not None
+        return self._res_index
+
+    @property
+    def res_columns(self) -> "Index":
+        return self.result_columns
 
     @property
     def columns(self) -> "Index":
@@ -298,12 +313,12 @@ def apply_standard(self):
                 return self.obj._constructor_sliced(result, index=labels)
 
         # compute the result using the series generator
-        self.apply_series_generator()
+        results = self.apply_series_generator()
 
         # wrap results
-        return self.wrap_results()
+        return self.wrap_results(results)
 
-    def apply_series_generator(self):
+    def apply_series_generator(self) -> ResType:
         series_gen = self.series_generator
         res_index = self.result_index
 
@@ -330,17 +345,15 @@ def apply_series_generator(self):
                 results[i] = self.f(v)
                 keys.append(v.name)
 
-        self.results = results
-        self.res_index = res_index
-        self.res_columns = self.result_columns
+        self._res_index = res_index
+        return results
 
-    def wrap_results(self):
-        results = self.results
+    def wrap_results(self, results: ResType) -> Union["Series", "DataFrame"]:
 
         # see if we can infer the results
         if len(results) > 0 and 0 in results and is_sequence(results[0]):
 
-            return self.wrap_results_for_axis()
+            return self.wrap_results_for_axis(results)
 
         # dict of scalars
         result = self.obj._constructor_sliced(results)
@@ -367,10 +380,9 @@ def result_index(self) -> "Index":
     def result_columns(self) -> "Index":
         return self.index
 
-    def wrap_results_for_axis(self):
+    def wrap_results_for_axis(self, results: ResType) -> "DataFrame":
         """ return the results for the rows """
 
-        results = self.results
         result = self.obj._constructor(data=results)
 
         if not isinstance(results[0], ABCSeries):
@@ -406,13 +418,13 @@ def result_index(self) -> "Index":
     def result_columns(self) -> "Index":
         return self.columns
 
-    def wrap_results_for_axis(self):
+    def wrap_results_for_axis(self, results: ResType) -> Union["Series", "DataFrame"]:
         """ return the results for the columns """
-        results = self.results
+        result: Union["Series", "DataFrame"]
 
         # we have requested to expand
         if self.result_type == "expand":
-            result = self.infer_to_same_shape()
+            result = self.infer_to_same_shape(results)
 
         # we have a non-series and don't want inference
         elif not isinstance(results[0], ABCSeries):
@@ -423,13 +435,12 @@ def wrap_results_for_axis(self):
 
         # we may want to infer results
         else:
-            result = self.infer_to_same_shape()
+            result = self.infer_to_same_shape(results)
 
         return result
 
-    def infer_to_same_shape(self) -> "DataFrame":
+    def infer_to_same_shape(self, results: ResType) -> "DataFrame":
         """ infer the results to the same shape as the input object """
-        results = self.results
 
         result = self.obj._constructor(data=results)
         result = result.T