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Re: Dynamically creating properties?

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On 10/28/2011 08:48 AM, DevPlayer wrote:
> On Oct 27, 3:59 pm, Andy Dingley<ding...@codesmiths.com>  wrote:
>> I have some XML, with a variable and somewhat unknown structure. I'd
>> like to encapsulate this in a Python class and expose the text of the
>> elements within as properties.
>>
>> How can I dynamically generate properties (or methods) and add them to
>> my class?  I can easily produce a dictionary of the required element
>> names and their text values, but how do I create new properties at run
>> time?
>>
>> Thanks,
>
>      class MyX(object):
>          pass
>      myx = myx()
>
>      xml_tag = parse( file.readline() )
>
>      # should be a valid python named-reference syntax,
>      # although any object that can be a valid dict key is allowed.
>      # generally valid python named reference would be the answer to
> your question
>      attribute = validate( xml_tag )
>
>      # dynamicly named property
>      setattr( myx, attribute, property(get_func, set_func, del_func,
> attr_doc) )
>
>      # "dynamicly named method"
>      # really should be a valid python named-reference syntax
>      myfunc_name = validate(myfunc_name)
>
>      def somefunc(x):
>          return x+x
>      # or
>      somefunc = lambda x: x + x
>
>      setattr( myx, myfunc_name, somefunc )
>
>
> So beaware of:
>      # \\\\\\\\\\\\\\\\\\\\\\\\\
>      setattr(myx, '1', 'one')
>
>      myx.1
>          File "<input>", line 1
>          x.1
>            ^
>      SyntaxError: invalid syntax
>
>      # \\\\\\\\\\\\\\\\\\\\\\\\\
>      x.'1'
>        File "<input>", line 1
>          x.'1'
>              ^
>      SyntaxError: invalid syntax
>
>      # \\\\\\\\\\\\\\\\\\\\\\\\\
>      x.__dict__['1']   # returns
>      'one'
>
>      x.__dict__        # returns
>      {'1': 'one'}
>
> So you should validate your variable names if you are getting them
> from somewhere.

XML does not allow attribute names to start with a number, so I doubt 
you need to worry about that. In addition, if you also need to 
dynamically access attributes and you have zero control of the name, you 
can use getattr().

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Thread

Dynamically creating properties? Andy Dingley <dingbat@codesmiths.com> - 2011-10-27 12:59 -0700
  Re: Dynamically creating properties? John Gordon <gordon@panix.com> - 2011-10-27 20:14 +0000
  Re: Dynamically creating properties? DevPlayer <devplayer@gmail.com> - 2011-10-27 14:48 -0700
    Re: Dynamically creating properties? DevPlayer <devplayer@gmail.com> - 2011-10-27 16:00 -0700
      Re: Dynamically creating properties? DevPlayer <devplayer@gmail.com> - 2011-10-27 16:15 -0700
        Re: Dynamically creating properties? DevPlayer <devplayer@gmail.com> - 2011-10-27 17:35 -0700
      Re: Dynamically creating properties? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-10-28 07:42 +0000
        Re: Dynamically creating properties? DevPlayer <devplayer@gmail.com> - 2011-10-30 07:11 -0700
    Re: Dynamically creating properties? Lie Ryan <lie.1296@gmail.com> - 2011-10-28 14:42 +1100

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