how to change the column heading in pandas code example

Example 1: rename column pandas

>>> df.rename(index={0: "x", 1: "y", 2: "z"})
   A  B
x  1  4
y  2  5
z  3  6

Example 2: rename column pandas

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