By using a : colon in the list index, you are asking for a slice, which is always another list. In Python you can assign values to both an individual item in a list, and to a slice of the list.
I have a piece of code here that is supposed to return the least common element in a list of elements, ordered by commonality: def getSingle(arr): from collections import Counter c = Counte...
The first, [:], is creating a slice (normally often used for getting just part of a list), which happens to contain the entire list, and thus is effectively a copy of the list. The second, list(), is using the actual list type constructor to create a new list which has contents equal to the first list.
The first way works for a list or a string; the second way only works for a list, because slice assignment isn't allowed for strings. Other than that I think the only difference is speed: it looks like it's a little faster the first way. Try it yourself with timeit.timeit () or preferably timeit.repeat ().
When reading, list is a reference to the original list, and list[:] shallow-copies the list. When assigning, list (re)binds the name and list[:] slice-assigns, replacing what was previously in the list. Also, don't use list as a name since it shadows the built-in.
List<String> L = new ArrayList<String>(); You should read that as "L is a kind of List that deals with String objects". When you start dealing with Factory classes, it is critical to deal with contracts rather than specific implementations. Factories produce objects of various types at runtime. Using generics is pretty easy (most of the time).
list[a:b:c], a is the starting index, b is the ending index and c is the optional step size. This will give you a list starting at index a (inclusive) and ending at index b (exclusive) picking elements at a step of c. For example,
If your list of lists comes from a nested list comprehension, the problem can be solved more simply/directly by fixing the comprehension; please see How can I get a flat result from a list comprehension instead of a nested list?. The most popular solutions here generally only flatten one "level" of the nested list. See Flatten an irregular (arbitrarily nested) list of lists for solutions that ...
The notation List<?> means "a list of something (but I'm not saying what)". Since the code in test works for any kind of object in the list, this works as a formal method parameter. Using a type parameter (like in your point 3), requires that the type parameter be declared. The Java syntax for that is to put <T> in front of the function. This is exactly analogous to declaring formal parameter ...
A List uses an internal array to handle its data, and automatically resizes the array when adding more elements to the List than its current capacity, which makes it more easy to use than an array, where you need to know the capacity beforehand.
