hasattr() vs try-except block to deal with non-existent attributes

Question

if hasattr(obj, 'attribute'):     # do somthing 

vs

try:     # access obj.attribute except AttributeError, e:     # deal with AttributeError 

Which should be preferred and why?

Answer 1

Any benches that illustrate difference in performance?

timeit it's your friend

$ python -mtimeit -s 'class C(object): a = 4 c = C()' 'hasattr(c, "nonexistent")' 1000000 loops, best of 3: 1.87 usec per loop $ python -mtimeit -s 'class C(object): a = 4 c = C()' 'hasattr(c, "a")' 1000000 loops, best of 3: 0.446 usec per loop $ python -mtimeit -s 'class C(object): a = 4 c = C()' 'try:  c.a except:  pass' 1000000 loops, best of 3: 0.247 usec per loop $ python -mtimeit -s 'class C(object): a = 4 c = C()' 'try:  c.nonexistent except:  pass' 100000 loops, best of 3: 3.13 usec per loop $         |positive|negative hasattr|  0.446 |  1.87  try    |  0.247 |  3.13 

Answer 2

hasattr internally and rapidly performs the same task as the try/except block: it's a very specific, optimized, one-task tool and thus should be preferred, when applicable, to the very general-purpose alternative.