Is there a way in Python to determine if an object has some attribute? For example:
>>> a = SomeClass() >>> a.someProperty = value >>> a.property Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: SomeClass instance has no attribute 'property'
How can you tell if
a has the attribute
property before using it?
if hasattr(a, 'property'): a.property
EDIT: See zweiterlinde's answer below, who offers good advice about asking forgiveness! A very pythonic approach!
The general practice in python is that, if the property is likely to be there most of the time, simply call it and either let the exception propagate, or trap it with a try/except block. This will likely be faster than
hasattr. If the property is likely to not be there most of the time, or you're not sure, using
hasattr will probably be faster than repeatedly falling into an exception block.
As Jarret Hardie answered,
hasattr will do the trick. I would like to add, though, that many in the Python community recommend a strategy of "easier to ask for forgiveness than permission" (EAFP) rather than "look before you leap" (LBYL). See these references:
try: doStuff(a.property) except AttributeError: otherStuff()
... is preferred to:
if hasattr(a, 'property'): doStuff(a.property) else: otherStuff()