Class instance in Python

Question

I have problem with using class instance in Python. Ive created a new class ora which inherit connect class from cx_Oracle package. When I try tu run this code I recive information

File "pyt.py", line 12, in myquery ora.myConnect.cursor() AttributeError: 'NoneType' object has no attribute 'cursor'

So Python cannote recognize that in ora.myConnect is stored reference to instance. I dont know what can be reason of this error and what its wrong with code.

from cx_Oracle import connect

class ora(connect):
  myConnect = None

  def __init__(self,connstr):    
    ora.myConnect = connect.__init__(self,connstr)


  def myquery(self):
      ora.myConnect.cursor()
      ora.myConnect.cursor.execute("SELECT * FROM table")
      ora.myConnect.cursor.close()   



connstr = 'user/passwd@host:port/sid' 
connection = ora(connstr)      
connection.myquery()                 
connection.close()

EDIT

Ive tried to replace ora to self but still Python dont have access to instance

from cx_Oracle import connect

class ora(connect):
  myConnect = None

  def __init__(self,connstr):    
    self.myConnect = connect.__init__(self,connstr)
  def myquery(self):
      self.myConnect.cursor()
      self.myConnect.cursor.execute("SELECT * FROM table")
      self.myConnect.cursor.close()

Error: self.myConnect.cursor() AttributeError: 'NoneType' object has no attribute 'cursor'

EDIT2 This code works without OOP, for me self.myConnect sholud reference to object instance and this object should contain method cursor()

import cx_oracle
connstr = 'user/passwd@host:port/sid' 
connection = cx_oracle.connect(connstr)                   
cursor = connection.cursor()                              
cursor.execute("SELECT * FROM table")
cursor.close()
connection.close()

self.myConnect = connect.__init__(self,connstr) is odd. It seems unlikely that the __init__ method should return a cursor. Are you sure you understand how the class you're extending is supposed to work? — beerbajay
– beerbajay, Commented Mar 13, 2012 at 23:11
Based on the documentation here I would say you're not really supposed to extend connect as you have done. Instead, just call cx_Oracle.connect() from your __init__ and save the connection as self.myConnect. — beerbajay
– beerbajay, Commented Mar 13, 2012 at 23:24
self.myConnect sholud return reference to object instance, for example without OOP this code works import cx_oracle connstr = 'user/passwd@host:port/sid' connection = cx_oracle.connect(connstr) cursor = connection.cursor() cursor.execute("SELECT * FROM table") cursor.close() connection.close() — browarq
– browarq, Commented Mar 13, 2012 at 23:29
Thanks @beerbajay Your method without inherit works also great thnks for help — browarq
– browarq, Commented Mar 13, 2012 at 23:48

beerbajay · Accepted Answer · 2012-03-13 23:33:16Z

2

It seems like you want self:

class ora(connect):
    myConnect = None

    def __init__(self, connstr):    
        self.myConnect = connect.__init__(self, connstr)

    # ...

ora is the name of the class, not the instance.

Update Try the following:

from cx_Oracle import connect

class ora:
    myConnect = None

    def __init__(self, connstr):    
        self.myConnect = connect(connstr)

    def myquery(self):
        self.myConnect.cursor()
        self.myConnect.cursor.execute("SELECT * FROM table")
        self.myConnect.cursor.close()

edited Mar 13, 2012 at 23:33

answered Mar 13, 2012 at 22:55

beerbajay

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2 Comments

beerbajay Over a year ago

If you replace ora with self in __init__ and myquery, your connection object should be functional. What error are you getting?

browarq Over a year ago

I had a problem with comments fromating, so I`ve added more details in first post

Daniel Roseman · Accepted Answer · 2012-03-13 23:37:53Z

1

Why do you want self.myConnect to refer to the connect instance? That's a complete misunderstanding of OOP. The ora instance is the connect instance. self.cursor is where you find the cursor.

Here's how your code should look:

class ora(connect):

  def __init__(self,connstr):    
    super(ora, self).__init__(connstr)

  def myquery(self):
    self.cursor.execute("SELECT * FROM table")
    self.cursor.close()

In any case, __init__ must never return anything, so setting self.myConnect to the return value will always result in it being bound to None.

answered Mar 13, 2012 at 23:37

Daniel Roseman

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1 Comment

browarq Over a year ago

Thanks - I don`t knew about this metod super, now it works great

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