Which is better in python, del or delattr?

python del
pydanny picture pydanny · Jul 13, 2009 · Viewed 92.3k times · Source

This may be silly, but it's been nagging the back of my brain for a while.

Python gives us two built-in ways to delete attributes from objects, the del command word and the delattr built-in function. I prefer delattr because it I think its a bit more explicit:

del foo.bar
delattr(foo, "bar")

But I'm wondering if there might be under-the-hood differences between them.

Answer

Miles picture Miles · Jul 13, 2009

The first is more efficient than the second. del foo.bar compiles to two bytecode instructions:

  2           0 LOAD_FAST                0 (foo)
              3 DELETE_ATTR              0 (bar)

whereas delattr(foo, "bar") takes five:

  2           0 LOAD_GLOBAL              0 (delattr)
              3 LOAD_FAST                0 (foo)
              6 LOAD_CONST               1 ('bar')
              9 CALL_FUNCTION            2
             12 POP_TOP

This translates into the first running slightly faster (but it's not a huge difference – .15 μs on my machine).

Like the others have said, you should really only use the second form when the attribute that you're deleting is determined dynamically.

[Edited to show the bytecode instructions generated inside a function, where the compiler can use LOAD_FAST and LOAD_GLOBAL]

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