For Common Lispers and probably Schemers, Python has some surprising semantics around scope and lifetime extent of variables. Three that leap out at me are: * function parameters with default values are NOT new bindings for each invocation, so a default value of [] changes if you destructively modify this list object in the function * loop variables are NOT distinct lexical variables. The binding gloms on to a variable in the function's scope, both changing that lexical binding and not creating a new one for the loop (that goes away when the loop's scope ends) * loop variables are NOT distinct bindings per iteration, leading to the surprising results below Bill -----Original Message----- From: python-dev-bounces+billchi=microsoft.com@python.org [mailto:python-dev-bounces+billchi=microsoft.com@python.org] On Behalf Of Bill Janssen Sent: Friday, June 30, 2006 6:31 PM To: Giovanni Bajo Cc: Phillip J. Eby; Ka-Ping Yee; Guido van Rossum; Tim Peters; python-dev@python.org Subject: Re: [Python-Dev] 2.5 and beyond
a = [] for i in range(10): ... a.append(lambda: i) ... print [x() for x in a] [9, 9, 9, 9, 9, 9, 9, 9, 9, 9]
Isn't this exactly what you'd expect? Maybe I've been writing Python for too long... :-). Bill _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/billchi%40microsoft.co m