py4e python3的sqlite3使用案例

统计所有邮件的发件人所属机构的出现次数，按照邮件域名计算：

1. 提取数据部分是常规的文件处理方法file.split()
2. 不同点在于把数据插入数据库，需要调用cursor()相关指令，注意插入的数据用占位符?替代。
3. commit()放在循坏外，提高速度。

import sqlite3

conn = sqlite3.connect('testdb.sqlite')
cur = conn.cursor()

cur.execute('DROP TABLE IF EXISTS Counts')

cur.execute('''
CREATE TABLE Counts (org TEXT, count INTEGER)''')

fname = input('Enter file name: ')
if (len(fname) < 1): fname = 'mbox-short.txt'
# fname = 'mbox.txt'

fh = open(fname)
for line in fh:
    if not line.startswith('From: '): continue
    pieces = line.split()
    email_full = pieces[1]
    org  = email_full.split('@')[1]    #organization name 
    cur.execute('SELECT count FROM Counts WHERE org = ? ', (org,))
    row = cur.fetchone()

# counting times of the org ocurrence 
    if row is None:
        cur.execute('''INSERT INTO Counts (org, count)
                VALUES (?, 1)''', (org,))
    else:
        cur.execute('UPDATE Counts SET count = count + 1 WHERE org = ?',
                    (org,))

conn.commit()

# have a check about the results 
sqlstr = 'SELECT org, count FROM Counts ORDER BY count DESC LIMIT 10'

for row in cur.execute(sqlstr):
    print(str(row[0]), row[1])

cur.close()

2018.4.25