Re: Dynamic Class Creation
In article <8d79f0cb-9c5b-4243-8891-a15fb311f...@z18g2000prh.googlegroups.com>, Josh English wrote: > > >Analog Science Fiction and Fact >Analog >Science Fiction >First Contact >Hard Science Fiction > >Stanley Schmidt, Editor >267 Broadway, 4th Floor >New York, NY 10007-2352 > >http://www.analogsf.com > > >A child element with text and an attribute or two, for example, pose a >problem. I can call Market.title but should I try Market.title.field >or Market.title_field. > >Multiple elements, such as keywords, are allowed in xml but harder to >map to the object. I don't know if I want to go create a list and >methods for accessing those keywords as a list, or redefine the rules >of my XML to not allow multiple child elements with the same tag. I >can't decide. You should always think "LIST!" any time you have the potential for multiple elements with the same semantic tag. Whether you do it as a list for all elements or as a combo dict/list is something you need to decide; the latter is faster in many ways but is more cumbersome: Market.title.keyword[1] (Instance attributes and dict keys are almost trivially convertible.) You would probably get some mileage out of looking at the ElementTree implementation. -- Aahz (a...@pythoncraft.com) <*> http://www.pythoncraft.com/ Why is this newsgroup different from all other newsgroups? -- http://mail.python.org/mailman/listinfo/python-list
Re: Dynamic Class Creation
Josh English wrote: Chris, Thanks. This worked for the attributes, but I think the tactic is still misleading. There are child elements I can't quite determine how to deal with: Analog Science Fiction and Fact Analog Science Fiction First Contact Hard Science Fiction Stanley Schmidt, Editor 267 Broadway, 4th Floor New York, NY 10007-2352 http://www.analogsf.com A child element with text and an attribute or two, for example, pose a problem. I can call Market.title but should I try Market.title.field or Market.title_field. Multiple elements, such as keywords, are allowed in xml but harder to map to the object. I don't know if I want to go create a list and methods for accessing those keywords as a list, or redefine the rules of my XML to not allow multiple child elements with the same tag. I can't decide. Then the address is a bit of a bear. In short, I have to figure out the whole object interface to the XML and how I want that to work. Have you heard of or considered PyXB (http://pyxb.sourceforge.net/)? Not that I've much experience with it, but you can use it to generate python code from XML Schema files, and, I think, WSDL definitions. It's a bit of a rabbit hole, but then isn't that half the fun! The following might give you the idea. You start with a Schema schema.xsd, generate a python module from it, then read in some XML with the generated classes to get your custom objects. schema.xsd -- http://www.josh.com/schema/0.1"; xmlns:xs="http://www.w3.org/2001/XMLSchema"; xmlns:josh="http://www.josh.com/schema/0.1";> maxOccurs="unbounded"/> minOccurs="0"/> minOccurs="0"/> genbindings.sh --- #!/bin/sh pyxbgen -u schema.xsd -m market_binding -r demo.py --- s = """ http://www.josh.com/schema/0.1"; code="anlg" tier="ProMarket" mail="True"> Analog Science Fiction and Fact Analog Science Fiction First Contact Hard Science Fiction Stanley Schmidt, Editor 267 Broadway, 4th Floor New York http://www.analogsf.com """ import xml.dom.minidom import market_binding market = market_binding.CreateFromDOM(xml.dom.minidom.parseString(s).documentElement) print market.tier print market.code print market.keyword assert len(market.keyword) == 3 print market.address.name print market.toxml() -- http://mail.python.org/mailman/listinfo/python-list
Re: Dynamic Class Creation
Chris, Thanks. This worked for the attributes, but I think the tactic is still misleading. There are child elements I can't quite determine how to deal with: Analog Science Fiction and Fact Analog Science Fiction First Contact Hard Science Fiction Stanley Schmidt, Editor 267 Broadway, 4th Floor New York, NY 10007-2352 http://www.analogsf.com A child element with text and an attribute or two, for example, pose a problem. I can call Market.title but should I try Market.title.field or Market.title_field. Multiple elements, such as keywords, are allowed in xml but harder to map to the object. I don't know if I want to go create a list and methods for accessing those keywords as a list, or redefine the rules of my XML to not allow multiple child elements with the same tag. I can't decide. Then the address is a bit of a bear. In short, I have to figure out the whole object interface to the XML and how I want that to work. Thanks for the suggestion. It is undeniably clever. Josh -- http://mail.python.org/mailman/listinfo/python-list
Re: Dynamic Class Creation
On Tue, Mar 16, 2010 at 9:49 AM, Jack Diederich wrote: > On Tue, Mar 16, 2010 at 2:18 AM, Chris Rebert wrote: >> On Mon, Mar 15, 2010 at 11:01 PM, Josh English >> wrote: >>> What's the best way to create these helper methods? > > You can either define a catch-all __getattr__ method to look them up > dynamically, or as Chris kinda-suggested write descriptors for the > individual elements. > > class Market(): > def __init__(self, elem): > self._elem = elem > def __getattr__(self, name): > try: > # I'm assuming this raises a KeyError when not found > return self._elem.get(name) > except KeyError: > return self._elem.find(name) > def __setitem__(self, name, value): did you mean __setattr__ here? > The getattr/setattr method is easier to understand and will handle > arbitrary elements; for the descriptors version you'll have to define > one for each tag that might be used on the class. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Dynamic Class Creation
On Tue, Mar 16, 2010 at 2:18 AM, Chris Rebert wrote:
> On Mon, Mar 15, 2010 at 11:01 PM, Josh English
> wrote:
>> I have a large program with lots of data stored in XML. I'm upgrading
>> my GUI to use ObjectListView, but with my data in XML, I don't have
>> regular objects to interact with the OLV. I do have an XML validator
>> that defines the structure of the XML elements, and I'm trying to
>> dynamically create a class to wrap the XML element.
>>
>> So, an element like:
>>
>>
>> Writers of the Future
>>
>>
>> I want to create a class like:
>>
>> class Market(object):
>> def __init__(self, elem):
>> self._elem = elem
>>
>> def get_code(self):
>> return self._elem.get('code')
>>
>> def set_code(self, value):
>> self._elem.set('code', value)
>>
>> def get_title(self):
>> return self._elem.find('title').text
>>
>> def set_title(self, value):
>> node = self._elem.find('title')
>> node.text = value
>>
>> Naturally, I don't want to hand code this for every interface but
>> would like to create them dynamically. (The laziness of programming, I
>> guess.)
>>
>> What's the best way to create these helper methods?
You can either define a catch-all __getattr__ method to look them up
dynamically, or as Chris kinda-suggested write descriptors for the
individual elements.
class Market():
def __init__(self, elem):
self._elem = elem
def __getattr__(self, name):
try:
# I'm assuming this raises a KeyError when not found
return self._elem.get(name)
except KeyError:
return self._elem.find(name)
def __setitem__(self, name, value):
# like __getitem__ but for setting
Chris' property maker function is almost like a descriptor class (how
properties are implemented under the hood), here's a refactoring
[untested]
class ElemGetProperty():
def __init__(self, name):
self.name = name
def __get__(self, ob, cls):
return ob._elem.get(self.name)
def __set__(self, ob, val):
ob._elem.set(self.name, val)
You could write one property class for each kind of element (get/find)
and then put them in your class like this
class Market():
code = ElemGetProperty('code')
title = ElemFindProeprty('title')
The getattr/setattr method is easier to understand and will handle
arbitrary elements; for the descriptors version you'll have to define
one for each tag that might be used on the class.
-Jack
--
http://mail.python.org/mailman/listinfo/python-list
Re: Dynamic Class Creation
On Mon, Mar 15, 2010 at 11:01 PM, Josh English
wrote:
> I have a large program with lots of data stored in XML. I'm upgrading
> my GUI to use ObjectListView, but with my data in XML, I don't have
> regular objects to interact with the OLV. I do have an XML validator
> that defines the structure of the XML elements, and I'm trying to
> dynamically create a class to wrap the XML element.
>
> So, an element like:
>
>
> Writers of the Future
>
>
> I want to create a class like:
>
> class Market(object):
> def __init__(self, elem):
> self._elem = elem
>
> def get_code(self):
> return self._elem.get('code')
>
> def set_code(self, value):
> self._elem.set('code', value)
>
> def get_title(self):
> return self._elem.find('title').text
>
> def set_title(self, value):
> node = self._elem.find('title')
> node.text = value
>
> Naturally, I don't want to hand code this for every interface but
> would like to create them dynamically. (The laziness of programming, I
> guess.)
>
> I have tried several solutions that I found on various forums, but
> they are all several years old.
>
> Questions:
>
> What's the best way to create these helper methods?
Nested functions:
def make_attr_getset(name):
def get(self):
return self._elem.get(name)
def set(self, value):
self._elem.set(name, value)
return get, set
get_code, set_code = make_attr_getset('code')
def make_subelement_getset(name):
def get(self):
return self._elem.find(name).text
def set(self, value):
node = self._elem.find(name)
node.text = value
return get, set
get_title, set_title = make_subelement_getset('title')
> How can I attach them to the class and have it run?
Use properties and setattr():
class Market(object):
def __init__(... #same as before
setattr(Market, 'code', property(get_code, set_code))
setattr(Market, 'title', property(get_title, set_title))
m = Market(the_XML)
print m.title #=> Writers of the Future
m.title = "Writers of the Past"
print m.code #=> WotF
m.code = "WofP"
Cheers,
Chris
--
http://blog.rebertia.com
--
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