All row sum with pandas except one
df['sum'] = df.drop('gid', axis=1).sum(axis=1)print (df) gid col2 col1 col3 sum0 6 15 45.0 77 137.01 1 15 45.0 57 117.02 2 14 0.2 42 56.23 3 12 6.0 37 55.04 4 9 85.0 27 121.05 5 5 1.0 15 21.0If gid is always first column, select by iloc all columns without first and then sum them:
df['sum'] = df.iloc[:, 1:].sum(axis=1)print (df) gid col2 col1 col3 sum0 6 15 45.0 77 137.01 1 15 45.0 57 117.02 2 14 0.2 42 56.23 3 12 6.0 37 55.04 4 9 85.0 27 121.05 5 5 1.0 15 21.0