Which is better in python, del or delattr?

• del is more explicit and efficient;
• delattr allows dynamic attribute deleting.

Consider the following examples:

for name in ATTRIBUTES:
    delattr(obj, name)

or:

def _cleanup(self, name):
    """Do cleanup for an attribute"""
    value = getattr(self, name)
    self._pre_cleanup(name, value)
    delattr(self, name)
    self._post_cleanup(name, value)

You can't do it with del.

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]