无法将Scrapy项目用作MySQL.execute的数据：“字符串格式化期间参数数量错误”

Question

I'm using Scrapy to parse content from a website into Items , which replicate the dict API:

import scrapy

class ScheduleItem(scrapy.Item):
    flight = scrapy.Field()

I'm trying to use the Item above directly as the data for a Connector/Python MySQLCursor.execute() statement using pyformat-style values. However, it's falling over with the following error:

(Pdb) add_schedule_sql()
'INSERT INTO schedules (flight) VALUES (%(flight)s)'

(Pdb) foo = items.ScheduleItem();
(Pdb) foo['flight'] = 'abc'
(Pdb) foo.keys()
['flight']
(Pdb) print foo
{'flight': 'abc'}
(Pdb) self.cursor.execute(add_schedule_sql(), foo)
*** ProgrammingError: Wrong number of arguments during string formatting

There's exactly one value to insert and exactly one value in the Item, both with the same key, so I'm rather baffled by this error. ( Source code here , which indicates it's actually hiding a TypeError.) If I use a plain old dict, it works fine:

(Pdb) bar = {'flight': 'abc'}
(Pdb) bar.keys()
['flight']
(Pdb) self.cursor.execute(add_schedule_sql(), bar)
(Pdb)

And if I map the item into a dict, the call also works fine:

(Pdb) self.cursor.execute(add_schedule_sql(), dict(item))
(Pdb)

The above is simple enough that it actually solves my problem adequately, but I'm still curious about what's wrong with just using an Item. Python 2.7.5, Scrapy 0.24 (latest stable).

Answer 1

The following works for me. So we need to see your implementation of ScheduleItem and also we need the version numbers of the libraries involved.

In [10]: class ScheduleItem(scrapy.Item):
flight = scrapy.Field()
delay = scrapy.Field()
....:     

In [11]: foo = ScheduleItem()

In [12]: foo['flight'] = 'abc'

In [13]: foo
Out[13]: {'flight': 'abc'}

In [14]: "test %(flight)s str"%(foo)
Out[14]: 'test abc str'

In [15]: "test (flight) and %(flight)s str"%(foo)
Out[15]: 'test (flight) and abc str'