CLN: clean Apply._try_aggregate_string_function (#53079)

* CLN: Apply._try_aggregate_string_function

* rename _try_aggregate_string_function -> _apply_string_function

---------

Co-authored-by: Richard Shadrach <45562402+rhshadrach@users.noreply.github.com>

Author: topper-123

pandas/core/apply.py

@@ -278,7 +278,7 @@ def transform_str_or_callable(self, func) -> DataFrame | Series:
         kwargs = self.kwargs
 
         if isinstance(func, str):
-            return self._try_aggregate_string_function(obj, func, *args, **kwargs)
+            return self._apply_str(obj, func, *args, **kwargs)
 
         if not args and not kwargs:
             f = com.get_cython_func(func)
@@ -543,7 +543,7 @@ def apply_str(self) -> DataFrame | Series:
                         self.kwargs["axis"] = self.axis
                 else:
                     self.kwargs["axis"] = self.axis
-        return self._try_aggregate_string_function(obj, f, *self.args, **self.kwargs)
+        return self._apply_str(obj, f, *self.args, **self.kwargs)
 
     def apply_multiple(self) -> DataFrame | Series:
         """
@@ -601,34 +601,32 @@ def normalize_dictlike_arg(
             func = new_func
         return func
 
-    def _try_aggregate_string_function(self, obj, arg: str, *args, **kwargs):
+    def _apply_str(self, obj, arg: str, *args, **kwargs):
         """
         if arg is a string, then try to operate on it:
-        - try to find a function (or attribute) on ourselves
+        - try to find a function (or attribute) on obj
         - try to find a numpy function
         - raise
         """
         assert isinstance(arg, str)
 
-        f = getattr(obj, arg, None)
-        if f is not None:
+        if hasattr(obj, arg):
+            f = getattr(obj, arg)
             if callable(f):
                 return f(*args, **kwargs)
 
-            # people may try to aggregate on a non-callable attribute
+            # people may aggregate on a non-callable attribute
             # but don't let them think they can pass args to it
             assert len(args) == 0
             assert len([kwarg for kwarg in kwargs if kwarg not in ["axis"]]) == 0
             return f
-
-        f = getattr(np, arg, None)
-        if f is not None and hasattr(obj, "__array__"):
+        elif hasattr(np, arg) and hasattr(obj, "__array__"):
             # in particular exclude Window
+            f = getattr(np, arg)
             return f(obj, *args, **kwargs)
-
-        raise AttributeError(
-            f"'{arg}' is not a valid function for '{type(obj).__name__}' object"
-        )
+        else:
+            msg = f"'{arg}' is not a valid function for '{type(obj).__name__}' object"
+            raise AttributeError(msg)
 
 
 class NDFrameApply(Apply):