get a column that corresponds to the average of two columns pandas

df['avg'] = df.mean(axis=1)

       Monday  Tuesday  Wednesday        avg
Mike       42      NaN         12  27.000000
Jenna     NaN      NaN         15  15.000000
Jon        21        4          1   8.666667

Here is what the above code is Doing:
1. We create a new column called ‘avg’ and set it equal to the mean of the other columns.
2. We use the axis=1 parameter to tell Python that we want to calculate the mean of each row, not column.
3. We use the inplace=True parameter to tell Python that we want to change our existing DataFrame, instead of creating a new one.