AttributeError：数据库实例没有属性＆＃39; _db＆＃39;

Question

我从互联网的某个地方复制了这段代码，我试图从一些视频教程学习python，我发现这段代码.. 当我试图用python2.7编译它时，它给出了下面的errro

错误-OUTPUT

  

在[23]中：％run＆＃34; C：\ Users \ Developer \ Canopy \ DevDir \ aaa.py＆＃34;

Create table test
AttributeError Traceback (most recent call last)

C:\Users\Developer\Canopy\DevDir\aaa.py in <module>()
    101     for row in db: print(row)
    102 
--> 103 if __name__ == "__main__": main()

C:\Users\Developer\Canopy\DevDir\aaa.py in main()
     78 
     79     print('Create table test')
---> 80     db.sql_do('drop table if exists test')
     81     db.sql_do('create table test ( t1 text, i1 int )')
     82 

C:\Users\Developer\Canopy\DevDir\aaa.py in sql_do(self, sql, *params)
     13 
     14     def sql_do(self, sql, *params):
---> 15         self._db.execute(sql, params)
     16         self._db.commit()
     17 

AttributeError: database instance has no attribute '_db' 

代码

#!/usr/bin/python3

import sqlite3

class database:
    def __init__(self, **kwargs):
        self.filename = kwargs.get('filename')
        self.table = kwargs.get('table', 'test')

    def sql_do(self, sql, *params):
        self._db.execute(sql, params)
        self._db.commit()

    def insert(self, row):
        self._db.execute('insert into {} (t1, i1) values (?, ?)'.format(self._table), (row['t1'], row['i1']))
        self._db.commit()

    def retrieve(self, key):
        cursor = self._db.execute('select * from {} where t1 = ?'.format(self._table), (key,))
        return dict(cursor.fetchone())

    def update(self, row):
        self._db.execute(
            'update {} set i1 = ? where t1 = ?'.format(self._table),
            (row['i1'], row['t1']))
        self._db.commit()

    def delete(self, key):
        self._db.execute('delete from {} where t1 = ?'.format(self._table), (key,))
        self._db.commit()

    def disp_rows(self):
        cursor = self._db.execute('select * from {} order by t1'.format(self._table))
        for row in cursor:
            print('  {}: {}'.format(row['t1'], row['i1']))

    def __iter__(self):
        cursor = self._db.execute('select * from {} order by t1'.format(self._table))
        for row in cursor:
            yield dict(row)

    @property
    def filename(self):
        return self._filename

    @filename.setter
    def filename(self, fn):
        self._filename = fn
        self._db = sqlite3.connect(fn)
        self._db.row_factory = sqlite3.Row

    @filename.deleter
    def filename(self): self.close()

    @property
    def table(self): return self._table
    @table.setter
    def table(self, t): self._table = t
    @table.deleter
    def table(self): self._table = 'test'

    def close(self):
            self._db.close()
            del self._filename

def main():
    db = database(filename = 'test.db', table = 'test')

    print('Create table test')
    db.sql_do('drop table if exists test')
    db.sql_do('create table test ( t1 text, i1 int )')

    print('Create rows')
    db.insert(dict(t1 = 'one', i1 = 1))
    db.insert(dict(t1 = 'two', i1 = 2))
    db.insert(dict(t1 = 'three', i1 = 3))
    db.insert(dict(t1 = 'four', i1 = 4))
    for row in db: print(row)

    print('Retrieve rows')
    print(db.retrieve('one'), db.retrieve('two'))

    print('Update rows')
    db.update(dict(t1 = 'one', i1 = 101))
    db.update(dict(t1 = 'three', i1 = 103))
    for row in db: print(row)

    print('Delete rows')
    db.delete('one')
    db.delete('three')
    for row in db: print(row)

if __name__ == "__main__": main()

  

没有缩进错误   我无法弄清楚如何使其发挥作用   任何帮助？

Answer 1

python2.7中的

属性不太优雅（这不是很好的编程imho。在构造函数中定义所有成员通常是好的做法;除其他外）：

import sqlite3

class database:
    def __init__(self, **kwargs):
        self._set_filename(kwargs.get('filename'))
        self._set_table( kwargs.get('table', 'test') )

    def sql_do(self, sql, *params):
        self._db.execute(sql, params)
        self._db.commit()

    def insert(self, row):
        self._db.execute('insert into {} (t1, i1) values (?, ?)'.format(self._table), (row['t1'], row['i1']))
        self._db.commit()

    def retrieve(self, key):
        cursor = self._db.execute('select * from {} where t1 = ?'.format(self._table), (key,))            print 'SETTER'
        return dict(cursor.fetchone())

    def update(self, row):
        self._db.execute(
            'update {} set i1 = ? where t1 = ?'.format(self._table),
            (row['i1'], row['t1']))
        self._db.commit()

    def delete(self, key):
        self._db.execute('delete from {} where t1 = ?'.format(self._table), (key,))
        self._db.commit()

    def disp_rows(self):
        cursor = self._db.execute('select * from {} order by t1'.format(self._table))
        for row in cursor:
            print('  {}: {}'.format(row['t1'], row['i1']))

    def __iter__(self):
        cursor = self._db.execute('select * from {} order by t1'.format(self._table))
        for row in cursor:
            yield dict(row)

    def _get_filename(self):
        return self._filename

    def _set_filename(self, fn):
        self._filename = fn
        self._db = sqlite3.connect(fn)
        self._db.row_factory = sqlite3.Row

    def _del_filename(self): self.close()

    filename = property(_get_filename, _set_filename, _del_filename)


    def _get_table(self): return self._table
    def _set_table(self, t): self._table = t
    def _del_table(self): self._table = 'test'

    table = property(_get_table, _set_table, _del_table)

    def close(self):
            self._db.close()
            del self._filename

def main():
    db = database(filename = 'test.db', table = 'test')

    print('Create table test')
    db.sql_do('drop table if exists test')
    db.sql_do('create table test ( t1 text, i1 int )')

    print('Create rows')
    db.insert(dict(t1 = 'one', i1 = 1))
    db.insert(dict(t1 = 'two', i1 = 2))
    db.insert(dict(t1 = 'three', i1 = 3))
    db.insert(dict(t1 = 'four', i1 = 4))
    for row in db: print(row)

    print('Retrieve rows')
    print(db.retrieve('one'), db.retrieve('two'))

    print('Update rows')
    db.update(dict(t1 = 'one', i1 = 101))
    db.update(dict(t1 = 'three', i1 = 103))
    for row in db: print(row)

    print('Delete rows')
    db.delete('one')
    db.delete('three')
    for row in db: print(row)

if __name__ == "__main__": main()