Python:按不同值对单列进行分组

Question

我有一个像这样的 sqlite 数据库，其中包含列标题和数据:

expiration, title
2015-08-15, example title
2015-08-15, another sample title
2015-08-15, another one
2015-08-16, lorem ipsum
2015-08-16, example

有没有一种方法可以按到期日期进行分组，这样会产生如下结果:

Expiring 2015-08-15
    example title
    another sample title
    another one
Expiring 2015-08-16
    lorem ipsum
    example

目前这是我所拥有的:

cur.execute("SELECT DISTINCT * FROM expiration WHERE exp BETWEEN date('now','-1 days') AND date('now','+6 days') ORDER BY exp")
    sql.commit()
    row = cur.fetchall()
    for res  in row:
        msg += res[1] + "\n"
    print msg

但它不按日期分组，它只是列出所有标题

Answer 1

你绝对可以在sql中实现这种分组操作，但是如果不深入研究sqlite细节，在python中也可以很容易地进行分组，如下所示:

import itertools as it

cur.execute("SELECT * FROM expiration WHERE exp BETWEEN date('now','-1 days') AND date('now','+6 days') ORDER BY exp")
sql.commit()
row = cur.fetchall()
for i,g in it.groupby(row, key=lambda x: x[0]):
    msg += 'Expiring %s%s\n' % (i, '\n\t'.join(x[1] for x in g))
print msg