CLN: aggregation.transform

Author: rhshadrach

pandas/core/aggregation.py

@@ -18,7 +18,7 @@
     Union,
 )
 
-from pandas._typing import AggFuncType, Axis, FrameOrSeries, Label
+from pandas._typing import AggFuncType, Axis, FrameOrSeries, FrameOrSeriesUnion, Label
 
 from pandas.core.dtypes.common import is_dict_like, is_list_like
 from pandas.core.dtypes.generic import ABCDataFrame, ABCSeries
@@ -387,8 +387,8 @@ def validate_func_kwargs(
 
 
 def transform(
-    obj: FrameOrSeries, func: AggFuncType, axis: Axis, *args, **kwargs,
-) -> FrameOrSeries:
+    obj: FrameOrSeriesUnion, func: AggFuncType, axis: Axis, *args, **kwargs,
+) -> FrameOrSeriesUnion:
     """
     Transform a DataFrame or Series
 
@@ -423,13 +423,13 @@ def transform(
         assert not is_series
         return transform(obj.T, func, 0, *args, **kwargs).T
 
-    if isinstance(func, list):
+    if is_list_like(func) and not is_dict_like(func):
         if is_series:
             func = {com.get_callable_name(v) or v: v for v in func}
         else:
             func = {col: func for col in obj}
 
-    if isinstance(func, dict):
+    if is_dict_like(func):
         if not is_series:
             cols = sorted(set(func.keys()) - set(obj.columns))
             if len(cols) > 0:
@@ -439,7 +439,7 @@ def transform(
             # GH 15931 - deprecation of renaming keys
             raise SpecificationError("nested renamer is not supported")
 
-        results = {}
+        results: Dict[Label, FrameOrSeriesUnion] = {}
         for name, how in func.items():
             colg = obj._gotitem(name, ndim=1)
             try:

pandas/core/shared_docs.py

@@ -267,14 +267,15 @@
 ----------
 func : function, str, list or dict
     Function to use for transforming the data. If a function, must either
-    work when passed a {klass} or when passed to {klass}.apply.
+    work when passed a {klass} or when passed to {klass}.apply. If func
+    is both list-like and dict-like, dict-like behavior takes precedence.
 
     Accepted combinations are:
 
     - function
     - string function name
-    - list of functions and/or function names, e.g. ``[np.exp, 'sqrt']``
-    - dict of axis labels -> functions, function names or list of such.
+    - list-like of functions and/or function names, e.g. ``[np.exp, 'sqrt']``
+    - dict-like of axis labels -> functions, function names or list-like of such.
 {axis}
 *args
     Positional arguments to pass to `func`.