python - 'str' object has no attribute 'execute'

Question

First time python user here, be gentle.... ;-)

Python 2.6 on OSX

Got a class which just has some wrappers around sqlite... here it is

from pysqlite2 import dbapi2 as sqlite

class SqliteDB:
    connection = ''
    curser = ''

    def connect(self):
        try:
            self.connection = sqlite.connect("pagespeed.sqlite")
            self.curser = self.connection.cursor()
         except sqlite.Error, e:
            print "Ooops: ", e.args[0]

    def find_or_create(self, table, column, value):
        self.curser.execute("SELECT id FROM ? WHERE ?=? LIMIT 1", (table, column, value))
        records = self.curser.fetchall()
        if records.count() == false:
            self.curser.execute("INSERT into ? SET ?=?", (table, column, value))
            self.curser.execute("SELECT id FROM ? WHERE ?=? LIMIT 1", (table, column, value))
        print records

and I call it like this in a separate file

import sqlitedb

def main():
    db = sqlitedb.SqliteDB()
    db.connect    
    url_id = db.find_or_create('urls', 'url', 'http://www.example.com')

however I get this error,

Traceback (most recent call last):

  File "update_urls.py", line 17, in <module>

  main()

  File "update_urls.py", line 11, in main

  url_id = db.find_or_create('urls', 'url', 'http://www.example.com')

  File "....../sqlitedb.py", line 16, in find_or_create

  self.curser.execute("SELECT id FROM ? WHERE ?=? LIMIT 1", (table, column, value))

AttributeError: 'str' object has no attribute 'execute'

So it's almost like self.curser is not getting a curser, or is self not correct?

Not to sure if what I am doing is right here....

cheers

You may think it amusing to use curser as a variable name but anyone who needs to read your code will be cursing your name as they nut through the code to detect whether it's a typo for cursor or not. — John Machin
– John Machin, Commented Oct 23, 2010 at 22:08
Sorry my mistake, I was going for cursor but my english is that bad... and it's my only language (english). Poor form to not know how to spell properly at my age. — Wizzard
– Wizzard, Commented Oct 23, 2010 at 23:16
Thanks all for the great feedback as well, just about to duck out for 10 mins and will check and award the answer when i'm back. I also VERY much appreciate the feedback on other sections of code, very helpful — Wizzard
– Wizzard, Commented Oct 23, 2010 at 23:22

extraneon · Accepted Answer · 2010-10-23 21:53:35Z

7

I don't know what's wrong, but at the very least:

db.connect

should be

db.connect()

e.g. call the function.

OK. S.Lott had the answer, I just found an other bug :)

answered Oct 23, 2010 at 21:53

extraneon

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7 Comments

aaronasterling Over a year ago

No... you found the bug, S. Lott found a nitpick. With his correction, OP will just get the same error but with NoneType instead of str.

aaronasterling Over a year ago

er, scratch that. OP would get an AttributeError. Popped into my head when thinking about something completely different. Ad it is good advice.

John Machin Over a year ago

@aaronsterling: Huh? You were right first time. Previously, self.curser refers to class attribute, value ''. After S.Lott change (but not fixing not calling connect method): instance attribute, value None. So: from AttributeError: 'str' object has no attribute 'execute' to AttributeError: 'NoneType' object has no attribute 'execute'

aaronasterling Over a year ago

@John Machin, no because the change moves the creation of connection and curser_sic into the connect method which is never called. When find_or_create is then called, you should get AttributeError: 'SqliteDB' object has not attribute 'curser_sic'. right? So it's still an Attribute error, just with a different attribute.

John Machin Over a year ago

@aaronsterling: You are correct as to outcome. @S.Lott moved the creation of those 2 into the __init__ method, which would be called, not the connect method. However @S.Lott also changed from curser_sic to cursor on the way to the __init__. Had he not done that, the outcome would have been as you suggested initially.

|

S.Lott · Accepted Answer · 2010-10-23 21:53:09Z

4

Do Not Do This.

class SqliteDB:
    connection = ''
    curser = ''

It doesn't "declare" any variables. This isn't C++ or Java.

Do this.

class SqliteDB:
    def __init__( self ):
        self.connection = None
        self.cursor= None

answered Oct 23, 2010 at 21:53

S.Lott

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2 Comments

Zooba Over a year ago

Actually, it declares class variables (accessible through self.connection or SqliteDB.connection). As soon as you write to self.connection you create an instance variable (meaning only SqliteDB.connection will access the class variable now).

S.Lott Over a year ago

Zooba: You're very close. It declares nothing. It creates class level variables that are concealed by instance variables. It's a common mistake.

John Machin · Accepted Answer · 2010-10-23 22:18:46Z

1

And the 3rd bug:

self.curser.execute("SELECT id FROM ? WHERE ?=? LIMIT 1", (table, column, value))

You can't parameterise table names and column names. All you can parameterise are things that can be an expression in SQL syntax. You'll need to do something like this:

sql = "SELECT id FROM %s WHERE %s = ? LIMIT 1" % (table, column)
self.curser.execute(sql, (value, ))

Oh yeah, to save the flurry of comments: or use the modern string.format(data) method instead of the antique string % data operator.

answered Oct 23, 2010 at 22:18

John Machin

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2 Comments

Wizzard Over a year ago

string.format(data) was python 3 I thought? I will recheck but from my OP I am using 2.6. Thanks for the feedback.

John Machin Over a year ago

and here's a link: docs.python.org/release/2.6/whatsnew/…

mouad · Accepted Answer · 2010-10-23 22:20:27Z

1

I will also add that this will not work :

curser.execute("SELECT id FROM ? WHERE ?=? LIMIT 1", (table, column, value))

because placeholders (?) doesn't work for table name, you should rather use string formatting before if you still want to use table name as parameter:

query = "SELECT id FROM %s WHERE %s=? LIMIT 1" % (table, column)
curser.execute(query, (value, ))

and one last thing "curser" is misspelled :)

answered Oct 23, 2010 at 22:20

mouad

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1 Comment

Wizzard Over a year ago

great thanks for the feedback, my poor spelling as well :) thnks for your time

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