"Clayton Kirkwood" <c...@godblessthe.us> Wrote in message: > > > !-----Original Message----- > !From: Tutor [mailto:tutor-bounces+crk=godblessthe...@python.org] On > !Behalf Of Dave Angel > !Sent: Tuesday, October 28, 2014 6:34 PM > !To: tutor@python.org > !Subject: Re: [Tutor] Would somebody kindly... > ! > ! > !> > ! Explain this double speak(>: > !> [pair for pair in values if key == pair[0]] > ! > !> I understand the ‘for pair in values’. I assume the first ‘pair’ > !> creates the namespace > ! > !The namespace question depends on the version of Python. Python 2.x > !does not do any scoping. > ! > !But in version 3.x, the variable pair will go away. > ! > !So please tell us the version you're asking about. > > I am using 3.4.1. >
Have you somehow configured your email program to use exclamation points for quoting instead of the standard greater-than symbol? "!" instead of ">" ? If so, do you mind changing it back? In 3.4.1, let's consider the following code. thingie = 2 mylist = [(2,55), "charlie", [2, "item2", 12]] x = [78 for item in mylist if item[0] == thingie] What will happen in the list comprehension, and what will be the final value of x ? First an anonymous list object will be created. This eventually will be bound to x, but not till the comprehension is successfully completed. Next a locally scoped variable item is created. This goes away at the end of the comprehension, regardless of how we exit. Next the 0th value from mylist is bound to item. It happens to be a tuple, but not from anything the comprehension decides. Next the expression item [0] == thingie is evaluated. If it's true, then the int 78 is appended to the anonymous list. Now the previous group of actions is repeated for the 1th value of mylist. So now item is a string, and the zeroth character of the string is compared with the int 2. Not equal, so 72 doesn't get appended. Similarly for the 2th item. The first element of that list is equal to 2, so another 72 is appended. Now the anonymous list is bound to x. print (x) [72, 72] -- DaveA _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
