>The same thing occurs when you use a mutable object like a list or a >dict. The default value is assigned once, and once only. But notice that >you can modify the default value, say by appending to it:
Not sure this will work exactly the same way in other IDEs, but in mine: >>> a = [] >>> def foo(x=a): ... x.append(1) ... >>> a.append( 2 ) >>> foo() >>> print a [2, 1] >>> help(foo) Help on function foo in module __pieshell__: foo(x=[2, 1]) >>> foo() >>> help(foo) Help on function foo in module __pieshell__: foo(x=[2, 1, 1]) >>> a.append( 3 ) >>> help(foo) Help on function foo in module __pieshell__: foo(x=[2, 1, 1, 3]) >>> b = [] >>> foo(b) >>> b [1] Notice how it is always bound to the list a, but can be "overridden". I know this has been discussed on this list or the main list before if you take a look through the archives. Sorry I can't remember what the thread would be like or when it was :( http://stackoverflow.com/questions/1132941/least-astonishment-in-python-the-mutable-default-argument Ramit Ramit Prasad | JPMorgan Chase Investment Bank | Currencies Technology 712 Main Street | Houston, TX 77002 work phone: 713 - 216 - 5423 This email is confidential and subject to important disclaimers and conditions including on offers for the purchase or sale of securities, accuracy and completeness of information, viruses, confidentiality, legal privilege, and legal entity disclaimers, available at http://www.jpmorgan.com/pages/disclosures/email. _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
