On Apr 22, 12:10 am, candide <cand...@free.invalid> wrote: > Suppose a and b are lists. > > What is more efficient in order to extend the list a by appending all > the items in the list b ? > > I imagine a.extend(b)to be more efficient for only appendinding the > items from b while a+=b creates a copy of a before appending, right ?
The a+=b form invokes list.__iadd__() which is implemented using list.extend(), so the two are basically the same. Looking at the source in http://svn.python.org/view/python/trunk/Objects/listobject.c?revision=78522&view=markup we see: static PyObject * list_inplace_concat(PyListObject *self, PyObject *other) { PyObject *result; result = listextend(self, other); if (result == NULL) return result; Py_DECREF(result); Py_INCREF(self); return (PyObject *)self; } There is a slight and constant difference is the overhead for making the call. The a.extend(b) does a dictionary lookup for the "extend" method and creates a bound method. Using a+=b is a little more direct. Raymond -- http://mail.python.org/mailman/listinfo/python-list
