Five. Python Slice __python

Part of the list is a very common element, now there is a set L = [' A ', ' B ', ' C ', ' D '], if the first 3 elements, the most primitive method is l[0], l[1], l[2], or with the loop out
R=[]
N=3
For I in range (n)
R.append (L)
Python provides us with a simpler way to get the slice slice operator, l[0:3], to achieve the same effect as the above, if the second and third elements are l[1:3].
If it is l[:] The equivalent of copying a new list set, L[::n] means that every n data is fetched. Change list to tuple, slice operation is identical, only slice of result also become tuple.
For the list, since Python supports l[-1] to take the penultimate element, it also supports reciprocal slices, l[-2:]=[' C ', ' D '],l[:-2]=[' A ', ' B '.

Similarly we can slice strings, string ' xxx ' and unicode string u ' xxx ' can also be considered as a list, each element is a character. Therefore, strings can also be sliced, but the result of the operation is still a string:

>>> ' ABCDEFG ' [: 3]
' ABC '
>>> ' ABCDEFG ' [-3:]
' EFG '
>>> ' ABCDEFG ' [:: 2]
' Aceg '

In many programming languages, many kinds of intercepting functions are provided for strings, but the goal is to slice the string. Python does not have an intercept function for a string, it is simple to slice one operation.