Re: Check existence of members/methods

From: Nicolas Fleury (nid_oizo_at_yahoo.com_remove_the_)
Date: 09/03/04 

Date: Thu, 02 Sep 2004 18:33:55 -0400

Nicolas Fleury wrote:

> Hi everyone,
> I'm wondering what is the easiest/cleanest way to look for existence
> of available methods/members.
>
> For example, in parsing a xml file, created objects can define a
> setXmlFilename function or a xmlFilename member to get the filename they
> are from.
>
> Right now I have the following code:
>
> try: object.setXmlFilename
> except:
> try: object.xmlFilename
> except: pass
> else: object.xmlFilename = currentFilename
> else: object.setXmlFilename(currentFilename)
>
> But it looks a bit wierd, since it's like a "if" with the false
> consequence presented first. I wonder if there is, and if there should
> be a better way to do it. I could also do the following:
>
> def noraise(expressionString):
> try: eval(expressionString)
> except: return True
> return False
>
> if noraise("object.setXmlFilename"):
> object.setXmlFilename(currentFilename)
> elif noraise("object.xmlFilename"):
> object.xmlFilename = currentFilename

In fact, it's even more ugly:

def exists(obj, name):
     try: eval("obj." + name)
     except: return True
     return False

if exists(object, "setXmlFilename"):
     object.setXmlFilename(currentFilename)
elif exists(object, "xmlFilename"):
     object.xmlFilename = currentFilename

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