On Mon, Dec 26, 2016 at 8:03 AM, Nick Timkovich <prometheus235@gmail.com> wrote:
Are you saying that hasattr returning False was hiding a bug or is a bug? The former could be annoying to track down, though hasattr(X, 'y') == True. For the latter, having hasattr return False if an AttributeError is raised would allow the property decorator to retain identical functionality if it is used to replace a (sometimes) existing attribute.
This was touched on during the StopIteration discussions, but left aside (it's not really connected, other than that exceptions are used as a signal). It's more that a property function raising AttributeError makes it look like it doesn't exist. Worth noting, though: The confusion only really comes up with hasattr. If you simply try to access the property, you get an exception that identifies the exact fault:
X().y Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 4, in y AttributeError: 'X' object has no attribute 'nonexisting'
Interestingly, the exception doesn't seem to have very useful arguments:
ee.args ("'X' object has no attribute 'nonexisting'",)
So here's a two-part proposal that would solve Zaheri's problem: 1) Enhance AttributeError to include arguments for the parts in quotes, for i18n independence. 2) Provide, in the docs, a hasattr replacement that checks the exception's args. The new hasattr would look like this: def hasattr(obj, name): try: getattr(obj, name) return True except AttributeError as e: if e.args[1] == obj.__class__.__name__ and e.args[2] == name: return False raise Since it's just a recipe in the docs, you could also have a version that works on current Pythons, but it'd need to do string manipulation to compare - something like: def hasattr(obj, name): try: getattr(obj, name) return True except AttributeError as e: if e.args[0] == "%r object has no attribute %r" % ( obj.__class__.__name__, name): return False raise I can't guarantee that this doesn't get some edge cases wrong, eg if you have weird characters in your name. But it'll deal with the normal cases, and it doesn't need any language changes - just paste that at the top of your file. Zaheri, would this solve your problem? ChrisA