Hello, On Wed, Oct 7, 2009 at 6:57 AM, Christer Edwards <christer.edwa...@gmail.com> wrote: > > do something to x for each x in list, with an optional qualifier. >
To be more precise: http://docs.python.org/tutorial/datastructures.html#list-comprehensions "Each list comprehension consists of an expression followed by a for clause, then zero or more for or if clauses" > On the other hand I've seen a few examples that look similar, but > there is no action done to the first x, which confuses me. An example: > > print sum(x for x in xrange(1,1000) if x%3==0 or x%5==0) So, it's not an 'action' as such, but an expression, x in this case is a variable containing a number, thus stating 'x' by itself is an expression that yields x's value and adds it to the sequence being generated without doing anything else to it. The built-in function sum (on the interpreter, type: help(sum)) takes a sequence of (numeric) values and returns their... sum :-). > In this case is sum() acting as the "action" on the first x? Can > anyone shed some light on what it is I'm not quite grasping between > the two? Hence, sum does not know about x at all, just about the end result of the generator expression: the generated sequence first evaluated, then passed into it as an argument. -- Kamal -- There is more to life than increasing its speed. -- Mahatma Gandhi _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
