Pandas: sum up multiple columns into one column without last column

You can first select by iloc and then sum:

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

For sum all columns use:

df['Fruit Total']= df.sum(axis=1)