Given a list items, that contains ints and None, produce a list that only
contains the int values with their order of appearance preserved.
Using filter
>>> items = [1, 2, None, 3, None, 4, 5, 6, None, 7]
>>> result = list(filter(bool, items))
>>> print(result)
[1, 2, 3, 4, 5, 6, 7]
Using list comprehensions
>>> items = [1, 2, None, 3, None, 4, 5, 6, None, 7]
>>> result = [i for i in items if i]
>>> print(result)
[1, 2, 3, 4, 5, 6, 7]
Using a for-loop
>>> items = [1, 2, None, 3, None, 4, 5, 6, None, 7]
>>> result = []
>>> for i in items:
... if i:
... result.append(i)
...
>>> print(result)
[1, 2, 3, 4, 5, 6, 7]
Using a recursive procedure
>>> items = [1, 2, None, 3, None, 4, 5, 6, None, 7]
>>> filter_stuff = lambda lst: ([lst[0]] if lst[0] else []) + (filter_stuff(lst[1:]) if lst[1:] else [])
>>> result = filter_stuff(items)
>>> print(result)
[1, 2, 3, 4, 5, 6, 7]
In-place
>>> items = [1, 2, None, 3, None, 4, 5, 6, None, 7]
>>> for i, e in enumerate(items):
... if not e:
... items.pop(i)
...
>>> print(items)
[1, 2, 3, 4, 5, 6, 7]