Fixed running install.py on a full track

[landrumb]

Currently, install.py does not build anything but the base dockerfile when you run it without specifying an algorithm, due to a bug on line 69.

The filter builtin actually returns an iterator over the results of a filtering of the input, not a collection containing them. Because iterators in python do not reset, the list comprehension using algos in line 72 of install.py has no elements after they're all consumed on the previous line, so dockerfiles is empty.

Demonstration of this idea:

>>> f = filter(lambda x: x % 2 == 0, list(range(50)))
>>> type(f)
<class 'filter'>
>>> x = [n for n in f]
>>> x
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48]
>>> y = [n for n in f]
>>> y
[]

zip(tags, dockerfiles) on line 94 has as many elements as its shortest argument, and therefore does nothing when you iterate over it in this case.

Building a list with the iterator created by filter solves this problem, because lists create a new iterator every time you try to iterate over them.

[maumueller]

Thanks @landrumb for the fix and the detailed description of the cause 💯