[Python-Dev] Re: A cute new way to get an infinite loop (original) (raw)

Beni Cherniavsky cben at users.sf.net
Thu Sep 23 19:24:35 CEST 2004

Tim Peters wrote:

x = [1] x.extend(-y for y in x) A simpler way:

x = [1, -1] x.extend(iter(x))

Curiously, this didn't "work" before 2.4 either:

x = [1] x.extend(iter(x)) x [1, 1]

The iterator did see the new elements after the extend call but not during it:

x = [1] i = iter(x) x.extend(x) list(i) [1, 1] x = [1] i = iter(x) x.extend([list(i)]) x [1, [1]]

The reason is that in 2.3 listextend() passed the right argument through PySequence_Fast which copied it before beggining to extend the list.

It's much better now. I mean it! Bugs should be predictable. Infinite loop should never terminate silently. Unless explicitly terminated.