CLN: Update pivot.py with fstrings (pandas-dev#29527)

All changes made for pivot.py + black pandas formatting.

Author: yashukla

pandas/core/reshape/pivot.py

@@ -193,7 +193,7 @@ def _add_margins(
     if not isinstance(margins_name, str):
         raise ValueError("margins_name argument must be a string")
 
-    msg = 'Conflicting name "{name}" in margins'.format(name=margins_name)
+    msg = f'Conflicting name "{margins_name}" in margins'
     for level in table.index.names:
         if margins_name in table.index.get_level_values(level):
             raise ValueError(msg)
@@ -620,9 +620,7 @@ def _normalize(table, normalize, margins, margins_name="All"):
         if (margins_name not in table.iloc[-1, :].name) | (
             margins_name != table.iloc[:, -1].name
         ):
-            raise ValueError(
-                "{mname} not in pivoted DataFrame".format(mname=margins_name)
-            )
+            raise ValueError(f"{margins_name} not in pivoted DataFrame")
         column_margin = table.iloc[:-1, -1]
         index_margin = table.iloc[-1, :-1]
 
@@ -672,7 +670,7 @@ def _get_names(arrs, names, prefix="row"):
             if isinstance(arr, ABCSeries) and arr.name is not None:
                 names.append(arr.name)
             else:
-                names.append("{prefix}_{i}".format(prefix=prefix, i=i))
+                names.append(f"{prefix}_{i}")
     else:
         if len(names) != len(arrs):
             raise AssertionError("arrays and names must have the same length")