On Fri, 09 Sep 2005 11:47:41 +0200, Jerzy Karczmarczuk wrote: > Gurus, before I am tempted to signal this as a bug, perhaps > you might convince me that it should be so. If I type > > l=range(4) > l.extend([1,2]) > > l gives [0,1,2,3,1,2], what else...
That is correct. range() returns a list. You then call the extend method on that list. Extend has deliberate side-effects: it operates on the list that calls it, it does not create a new list. > On the other hand, try > > p=range(4).extend([1,2]) > > Then, p HAS NO VALUE (NoneType). p has the value None, which is also correct. The extend() method returns None, it does not create a new list. There is nothing inconsistent about it. Unintuitive, perhaps. Unexpected, maybe. But not inconsistent. [snip] > WHY? Because creating a new list is potentially very time-consuming and expensive of memory. Imagine you have a list of 100,000 large objects, and you want to add one more object to it. The way Python works is that append and extend simply add that new object to the end of the existing list. The way you imagined it would work would require Python to duplicate the entire list, all 100,000 large objects, plus the extra one. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
