On Sunday, November 23, 2014 8:28:16 PM UTC+5:30, Ivan Evstegneev wrote: > Hello guys, > > I would like to ask you for some explanations on comprehensions. (Don't be > scared, it just some particular example ^_^) > > I found this little "find prime number" example over the internet: > > >>> noprimes = [j for i in range(2, 8) for j in range(i*2, 50, i)] > >>> primes = [x for x in range(2, 50) if x not in noprimes] > >>> print primes > [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47] > > > It looked pretty clear to me, till the time I decided to make some changes > to it %))) > > Ok this is the case: > > As you can see the first line's comprehension produces a list, that includes > all the multiplications of "i" (that range(2,8) ) in range (i*2, 50, i). > So I get this pattern: noprimes = = [4, 6, 8.....48, 6, 9,12.... ]. > The change that I tried to apply to this comprehension would lead to the > following pattern: noprimes = = [[4, 6,8...48], [6, 9, 12....], ....,[some > numbers]] > > But despite my struggling on it for the whole day, I haven't got to the > desirable result(using comprehensions only) > > Please, don't get me wrong, I'm not a lazy one (just a beginner). > > In my case, I made some googling, and found some patterns for matrices, that > look this one(for example): > > Matrix = [[0 for x in range(5)] for x in range(5)] > > But when I tried to use square brackets with my code, it yields an error > about definition of "i", for instance: > > File "<pyshell#30>", line 1, in <module> > noprimes = [[j for i in range(2, 8)] for j in range(i*2, 50, i)] > NameError: name 'i' is not defined.
Is this what you want? >>> [[j for j in range(i*2, 50, i)] for i in range(2,8)] [[4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48], [6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48], [8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48], [10, 15, 20, 25, 30, 35, 40, 45], [12, 18, 24, 30, 36, 42, 48], [14, 21, 28, 35, 42, 49]] [I am not sure what you are trying -- just making local changes to the ZF to make it work] -- https://mail.python.org/mailman/listinfo/python-list
