I can not understand how and why the first time it is printed a reference of the object(which object is referring to?) and the second time when I use two variables, these variables get the result of the function instead of a reference.
>>> a = map(int,[1,2])
>>> a
<map object at 0x7f0b1142fa90>
>>> b,c = a
>>> b
1
>>> c
2
In Python 3, map (and other primitive combinators) return an iterator object rather than a list (as they did before.) At the first attempt, you printed that iterator object per se, while the second time you matched it against a sequence, thus forcing and extracting elements. Consider:
>>> a = map(int,[1,2])
>>> a
<map object at 0x7ff6ddbfe748>
>>> list(a)
[1, 2]
primitive combinators? I'm not familiar with this term.
map, zip, etc. Many more of these are defined in the itertools library, and they are very common in functional languages. The general way to think of these is that you have some generic action you want to take on one or more lists, and the combinators provide a generic way to do it. I.e. mapping an arbitrary function lazily over an iterator (map).
map and filter. zip and reversed, e.g., work the same way: they used to return lists before, but now return iterators.primitive combinators. How is map "primitive" or a "combinator"? I think combinator is a term used in functional programming for a type of higher order function. Primitive I can't really pinpoint.
reversed used to return a list did it?