Unable to change a column name in a dataframe

Question

I'm working on some survey data and am looking to graph some of the results with standard deviation.

I can successfully create the new column with the std values, but it names the column (Question 3, std). I've then tried to rename the column 'std', but the column name doesn't change.

new_df = df.groupby('Respondants')[['Question 3']].agg({'std'})
std_df = df.merge(new_df, left_on=['Respondants'], right_index=True)
col_dict = {'Question 3': 'std'} 
std_df.columns = [col_dict.get(x, x) for x in std_df.columns]

What am I missing?

EDIT: The strange thing is that I've now tried:

new_df = df.groupby('Respondants')[['Question 3']].agg({'std'})
std_df = df.merge(new_df, left_on=['Respondants'], right_index=True)
std_df.rename(columns={'(Question 3, std)': 'std'}, inplace=True)
std_df.head(200)

and the result is the same. But if I try:

new_df = df.groupby('Respondants')[['Question 3']].agg({'std'})
std_df = df.merge(new_df, left_on=['Respondants'], right_index=True)
std_df.rename(columns={'Question 1': 'whatever'}, inplace=True)
std_df.head(200)

That column name changes, so the code works, but not for the column that I needed.

Answer 1

Use rename function of the DataFrame:

std_df.rename(columns={'(Question 3, std)': 'std'}, inplace=True)