Q.Which of the following Python statements is used to change a column label in a DataFrame, df? (A) df = df.rename({old_name: new_name}, axis='columns') (B) df = df.rename(old_name, new_name), axis='columns' (C) df = df.change_name(old_name, new_name, axis='bar') (D) df = df.update({old_name: new_name}, axis='bar')

rename() with a {old: new} dictionary and axis='columns' is the pandas way to change a column label; the result must be reassigned to df. (B) has a syntax error (arguments outside the call), (C) uses a non-existent change_name() method, and (D)'s update() changes values, not labels.

Concept — renaming a column label in pandas

A DataFrame's column names live in its column index. To change one, pandas provides the rename() method, which accepts a dictionary mapping ({old: new}) and an axis argument ('columns' or 1 for column labels). rename() returns a new DataFrame, so the result must be reassigned back to df.

import pandas as pd

df = pd.DataFrame({'old_name': [1, 2, 3]})
df = df.rename({'old_name': 'new_name'}, axis='columns')
print(df)

Expected output:

   new_name
0         1
1         2
2         3

Why each other option is wrong

• (B) df = df.rename(old_name, new_name), axis='columns' — rename() does not take old and new names as two positional arguments, and the stray , axis='columns' sits outside the call's parentheses, which is a syntax error (it would build a tuple, not pass a keyword argument). …