df['Fruit Total']= df.iloc[:, -4:-1].sum(axis=1)

print (df)

   Apples  Bananas  Grapes  Kiwis  Fruit Total

0     2.0      3.0     NaN    1.0          5.0

1     1.0      3.0     7.0    NaN         11.0

2     NaN      NaN     2.0    3.0          2.0

df = df['Day'].map(str) + '-' + df['Month'].map(str) + '-' + df['Year'].map(str)

​

sum_column = df["col1"] + df["col2"]

df['sum'] = df['a'] + df['b']  # sum is a new column

df['column_new_1'], df['column_new_2'], df['column_new_3'] = [np.nan, 'dogs', 3]

df1 = df['1st Column Name'].map(str) + df['2nd Column Name'].map(str) + ...

​