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comp.lang.python

hide object property from dir() function?

jerryji

1/14/2008 9:20:00 PM

Hi,

Sorry for this newbie question, I was puzzled why the existing
property of an object is not shown in the dir() function output.

"v" is an lxml Element object variable --

In [44]: v
Out[44]: <Element 'documentProperties' at 0x8363cf8>

In [45]: dir(v)
Out[45]:
['__copy__',
'__deepcopy__',
'__reduce__',
'append',
'clear',
'find',
'findall',
'findtext',
'get',
'getchildren',
'getiterator',
'insert',
'items',
'keys',
'makeelement',
'remove',
'set']

dir() output doesn't contain the ".tag", which does exist --

In [46]: v.tag
Out[46]: 'documentProperties'

what is the rule governing the display of a property from dir()?

Many thanks in advance!

Jerry
3 Answers

Matt McCredie

1/14/2008 9:51:00 PM

0

On Jan 14, 1:20 pm, jerryji <jerryji1...@gmail.com> wrote:
> Hi,
>
> Sorry for this newbie question, I was puzzled why the existing
> property of an object is not shown in the dir() function output.
>
> "v" is an lxml Element object variable --
>
> In [44]: v
> Out[44]: <Element 'documentProperties' at 0x8363cf8>
>
> In [45]: dir(v)
> Out[45]:
> ['__copy__',
> '__deepcopy__',
> '__reduce__',
> 'append',
> 'clear',
> 'find',
> 'findall',
> 'findtext',
> 'get',
> 'getchildren',
> 'getiterator',
> 'insert',
> 'items',
> 'keys',
> 'makeelement',
> 'remove',
> 'set']
>
> dir() output doesn't contain the ".tag", which does exist --
>
> In [46]: v.tag
> Out[46]: 'documentProperties'
>
> what is the rule governing the display of a property from dir()?


You can also make properties by modifying the __getattr__ and
__setattr__ methods of a class. When done that way it won't show up
when dir is called. So it isn't necessarily a rule, just a different
way of implementing a property.

Matt

Tim Golden

1/15/2008 9:06:00 AM

0

jerryji wrote:
> Sorry for this newbie question, I was puzzled why the existing
> property of an object is not shown in the dir() function output.

The under-development version of Python (2.6) allows for a
__dir__ magic method by which the class implementer can
return whatever he wishes from a dir (). This is to help,
for example, modules like my WMI one which makes heavy use
of __getattr__ magic to proxy across Windows COM attributes.
This, in turn, helps editors and IDEs which can provide
popup lists of attributes etc.

All that said, I don't believe it takes any automatic
account of properties.

TJG

<noddy code example>
class X (object):
def __init__ (self, a):
self.a = a

print dir (X (1))

def __dir__ (self):
return ['x', 'y', 'z']

X.__dir__ = __dir__

print dir (X (2))

</code>

Bobby Conover

2/8/2011 1:56:00 AM

0

It's really hard to pit Funhouse against any other pin because its
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it's very easy to fall in love with it despite its pretty shallow
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NGG has more to shoot for, better flow, fun toys, etc, and it's
definitely one I want to pick up someday. I wouldn't say it's a
classic like Funhouse, but it probably has more "staying power" if
sheer volume of stuff to do is your main concern. For me, Funhouse
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that feels unlike all others.