df['core'] = df1[(df['date'] > '2000-6-1') & (df['date'] <= '2000-6-10')]

df.loc[[0,3],'Z'] = 3

for index, row in df.iterrows():
    print(row['c1'], row['c2'])


for index1, row1 in df.iterrows():
    for index2 row2 in df1.iterrows():
        df['core'] += df1[(df['date'] > df1['reservation']) & (df['date'] <= df1['enddate'])]