how to change data frame element in python code example

Example 1: replace column values pandas

df['column'] = df['column'].str.replace(',','-')
df

Example 2: replace value of dataframe with another column

df['col1'] = np.where(df['col1'] == 0, df['col2'], df['col1'])
df['col1'] = np.where(df['col1'] == 0, df['col3'], df['col1'])