Question

Hi!
There's a line (or two identical ones) that i don't understand in the sample solution to Pset8.
here's my solution:
http://dpaste.com/782865/
and the sample one:
http://dpaste.com/782866/
1: why have they commented out and replaced line 11?
2: what's with lines 7 and 16? avoiding some type of problem?
Thanks!

Answer 1

what data type does virus.reproduce() return? line 11 looks like it should work. I wonder if it is a quirk in the interpreter and lines 12 and 13 force execution order.

lines 7 and 16 are using list comprehensions (which are very cool) ... what datatype is newViruses?? they might be doing that to make a completely separate/new copy of newViruses. - there are other ways to accomplish that.

Answer 2

Hey!
reproduce() returns an instance of the ResistantVirus class, and newViruses is just a list of such viruses after some method, like doesClear() is used on them. the sample solution switches between viruses and newViruses twice and i don't really understand why.
Yeah list comprehensions seem cool, but what's the use here? isn't it equivalent to viruses = newViruses? oh, and does it matter in which side of the "=" smthg is? ie is (viruses = newViruses) = (newViruses = viruses)?

Answer 3

as a matter of fact, it's a bit too cool..: how should i interpret
[[row[i] for row in matrix] for i in range(4)]
[[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]
that transposes a 3x4 matrix?

Answer 4

using a list comprehension gives you a completely separate object than the original list. sometimes this matters. http://dpaste.com/783441/
http://henry.precheur.org/python/copy_list
http://effbot.org/zone/python-list.htm
http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#other-languages-have-variables

not sure what you are asking but that list comprehension will transpose a 4x3 to a 3x4. (or whatever) http://dpaste.com/783444/