rename columns with loop

I’m trying to rename columns in a df with a for-loop.

Where am I going wrong with below?

for col_name in df:
    df.rename(columns={col_name:col_name + '_x'})

df now:

Desired result:

>Solution :

You can use list comprehension with pandas.DataFrame.columns :

df.columns = [col + "x" for col in df.columns]

Or simply :

df.columns = df.columns + "x"