how to replace a header name to a new name in pandas code example

Example 1: rename column pandas

>>> df.rename(columns={"A": "a", "B": "b", "C": "c"}, errors="raise")
Traceback (most recent call last):
KeyError: ['C'] not found in axis

Example 2: rename column pandas

>>> df.rename(str.lower, axis='columns')
   a  b
0  1  4
1  2  5
2  3  6