Lucas G. Sánchez Lucas G. Sánchez - 3 months ago 9
Python Question

How to know if an object has an attribute in Python

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?

Answer

Try hasattr():

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.

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