Which is better in python, del or delattr?

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]

• 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.

Unquestionably the former. In my view this is like asking whether foo.bar is better than getattr(foo, "bar"), and I don't think anyone is asking that question :)