On Sat, May 10, 2014 at 12:10 PM, Ethan Furman <et...@stoneleaf.us> wrote: > On 05/10/2014 02:32 AM, Chris Angelico wrote: >> >> >> Tell me, what may this function do in a compliant Python? >> >> def demo(): >> ret = spam >> spam = 23 >> return ret >> >> In CPython, that'll raise UnboundLocalError, because the local >> variable 'spam' does already exist, and currently has no value (no >> object bound to it). > > > No, it does not exist -- or, more accurately, it does not exist *yet* but > will. The fact that there is a slot waiting for what will be spam is a > cpython implementation detail.
The name of the exception is "UnboundLocalError". And the message says that we referred to a "local variable". Also see the language reference: "When a name is not found at all, a NameError exception is raised. If the name refers to a local variable that has not been bound, a UnboundLocalError exception is raised. UnboundLocalError is a subclass of NameError." spam is referring to a local variable that has not been bound. This is not an implementation detail. > And if you don't like that argument (although it is a perfectly sound and > correct argument), think of the module name space: > > > ret = spam > spam = 23 > > will net you a simple NameError, because spam has not yet been created. Because module level variables work differently from local variables. -- Devin -- https://mail.python.org/mailman/listinfo/python-list
