On Monday 30 November 2009 12:22:17 pm Manuel Graune wrote: > > when using local variables in list comprehensions, say > > a=[i for i in xrange(10)] > > the local variable is not destroyed afterwards: [...] > b=list(j for j in xrange(10)) > > the local variable is destroyed after use:
Actually, [] and list() are not the same. For instance, list(1,2) rises an error, while [1,2] is the list with two elements. The comprehension is just a syntactic contruct that allows you to simplify the creation of lists, while the list() "function" (it is a class, actually) receives an iterable object and returns a list. What you seem to be confused about is the construct: (j for j in xrange(10)) That is called a generator expression, and it is very similar to the list comprehension, except that it builds an iterator (instead of a list, i.e, the xrange(10) is not consumed until it is needed), and the loop variable doesn't "leak" outside. When you do b=list(j for j in xrange(10)), you are actually doing b=list((j for j in xrange(10))) (note the extra set of parenthesis - python lets you ommit those), i.e, you are calling the list() "function" with a single argument, an iterable that contains all the elements of xrange(10). You could be calling foobar(j for j in xrange(10)) instead. And I think I lost my way... I'm sleepy. If I confused you, sorry... and if I'm helped you, thank you for letting me :D. Cya. -- Luis Zarrabeitia (aka Kyrie) Fac. de Matemática y Computación, UH. http://profesores.matcom.uh.cu/~kyrie -- http://mail.python.org/mailman/listinfo/python-list
