Factory pattern again

[Mike Howarth]

Hi

I was wondering whether anyone could help me, I'm pretty new to python
coming from a PHP background and I'm having a few products in getting my
head round how to write the factory pattern within python.

I'm currently looking to try to return values from a db and load up the
relevant objects, values returned are product type (I,S) and product code
(123).

At the moment I've adapted some code I've found illustrating the factory
method but ideally I would like to use the type to load up the relevant
object.

Another issue I've found is that I don't seem to be able to access to the
price attribute of each of the object. I'm sure these are very
straightforward issues however I seem to have tied myself in knots over this
and could do with a fresh set of 'pythonic' eyes to help me out.

registry = {}

class MetaBase(type):
def __init__(cls, name, bases, dict):
registry[name] = cls

class Product(object):
__metaclass__ = MetaBase

class Item(Product):
def __init__(self, *args, **kw):
self.price = 1

class Set(Product):
def __init__(self, *args, **kw):
self.price = 2

def factory(kind, *args, **kw):
return registry[kind](*args, **kw)
item = registry['Item']
print item.price

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[Bruno Desthuilliers]

Mike Howarth a écrit :

Hi

I was wondering whether anyone could help me, I'm pretty new to python
coming from a PHP background and I'm having a few products in getting my
head round how to write the factory pattern within python.

I'm currently looking to try to return values from a db and load up the
relevant objects, values returned are product type (I,S) and product code
(123).

At the moment I've adapted some code I've found illustrating the factory
method but ideally I would like to use the type to load up the relevant
object.

Another issue I've found is that I don't seem to be able to access to the
price attribute of each of the object. I'm sure these are very
straightforward issues however I seem to have tied myself in knots over this
and could do with a fresh set of 'pythonic' eyes to help me out.

registry = {}

class MetaBase(type):
def __init__(cls, name, bases, dict):
registry[name] = cls

class Product(object):
__metaclass__ = MetaBase

class Item(Product):
def __init__(self, *args, **kw):
self.price = 1

class Set(Product):
def __init__(self, *args, **kw):
self.price = 2

def factory(kind, *args, **kw):
return registry[kind](*args, **kw)
item = registry['Item']

This returns the Item *class*, not an instance of... So the following:

print item.price

cannot work, since price is an instance attribute, not a class attribute.

What you want is:

item = factory('Item')
print item.price

HTH

[Mike Howarth]

Thanks that makes absolute sense.

I was sure it was something simple, thanks for your time.
Bruno Desthuilliers-5 wrote:

Mike Howarth a écrit :

>Hi

I was wondering whether anyone could help me, I'm pretty new to python
coming from a PHP background and I'm having a few products in getting my
head round how to write the factory pattern within python.

I'm currently looking to try to return values from a db and load up the
relevant objects, values returned are product type (I,S) and product code
(123).

At the moment I've adapted some code I've found illustrating the factory
method but ideally I would like to use the type to load up the relevant
object.

Another issue I've found is that I don't seem to be able to access to the
price attribute of each of the object. I'm sure these are very
straightforward issues however I seem to have tied myself in knots over
this
and could do with a fresh set of 'pythonic' eyes to help me out.

registry = {}

class MetaBase(type):
def __init__(cls, name, bases, dict):
registry[name] = cls

class Product(object):
__metaclass__ = MetaBase

class Item(Product):
def __init__(self, *args, **kw):
self.price = 1

class Set(Product):
def __init__(self, *args, **kw):
self.price = 2

def factory(kind, *args, **kw):
return registry[kind](*args, **kw)


item = registry['Item']

This returns the Item *class*, not an instance of... So the following:

>print item.price

cannot work, since price is an instance attribute, not a class attribute.

What you want is:

item = factory('Item')
print item.price

HTH
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[Steve Holden]

cu******@yahoo.com.cn wrote:

first you need find the bottleneck of your script db or function
if the bottleneck is db
1. which db do you use do you optimize the db from read
2. the sql you write do not use any index "maybe select code, type
from products where type = 'I' or type = 'S' will help" and you need
create index on type field maybe you need set limit 2000 to sql depend
on your requirement

Whether a relational database is indexed or not the SQL to retrieve
information from it will be exactly the same - the whole point if
indexing is that it represents a change to the physical schema that
improves retrieval efficiency without altering the logical schema.

Mike stated quite clearly "the db is normalized and indexes exist".

regards
Steve
--
Steve Holden [phone] [phone]
Holden Web LLC/Ltd http://www.holdenweb.com
Skype: holdenweb http://del.icio.us/steve.holden
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