python dataframe groupby

# -*- coding: UTF-8 -*-
import pandas as pd
df = pd.DataFrame([{'col1':'a', 'col2':1, 'col3':'aa'}, {'col1':'b', 'col2':2, 'col3':'bb'}, {'col1':'c', 'col2':3, 'col3':'cc'}, {'col1':'a', 'col2':44, 'col3':'aa'}])

print df.groupby(by='col1').agg({'col2':sum}).reset_index()
print df.groupby(by='col1').agg({'col2':['max', 'min']}).reset_index()
print df.groupby(by=['col1', 'col3']).agg({'col2':sum}).reset_index()

col1  col2
0    a    45
1    b     2
2    c     3
col1 col2
max min
0    a   44   1
1    b    2   2
2    c    3   3
col1 col3  col2
0    a   aa    45
1    b   bb     2
2    c   cc     3