Python: Slice character

Python's slice Character: (:) 1, single-slice character

Python's slice characters are used for tuples, strings, or lists, using left-hand open, which contains the nth number on the left side of the colon, not the number on the right, and the following as an example of a column:

>>> a=[1,2,3,4]>>> a[1:][2, 3, 4]>>> a[1:3][2, 3]>>> a[:3][1, 2, 3]>>>

2. Double-slice characters

Double slices: (::) is generally used to take a few of the elements or a set of strings, such as a list, the wording is also very flexible, the following explanation:

1) [:: N],n can be positive or negative, minus is the right-to-left, the absolute value of N represents how many to take one, the following is an example of a string:

>>> a="ABCDEFG">>> a[::-1]'GFEDCBA'>>> a[::-2]'Geca'>>> A[::2]'Aceg'>>> A[::3]'ADG'>>> A[::6]'AG'>>> A[::9]'a'

2) [M::n],m, N can be positive or negative, the following specific implementation:

I, when N is positive, is considered [m:][::n], as follows:

>>> a= (1,2,3,4,5,6,7) >>> A[3::2] (4, 6) >>> A[3:][::2] (4, 6)

2, when N is negative, as the first M-bit in the opposite direction of all values (including the first M bit), and then the [:: N] Operation

>>> a= (1,2,3,4,5,6,7) >>> A[4::-2] (5, 3, 1)

The above is the No. 0 to 4th bit of a is taken out, the result is (1,2,3,4,5), and then the [:: N] operation, the end result is (5,3,1), M is negative when the same, here is not added to the

3) [m:n:k] M, N can be positive or negative, K is positive:

>>> a= (1,2,3,4,5,6,7)>>> a[2:-2:3] (3,)

A take [2:-2], the result is (3,4,5), then every 3 to take one, the result is (3,) as for the following comma, is to indicate that this is a tuple, rather than a separate 3

3) [m:n:k] M, N can be positive or negative, K is negative:

>>> a=[1,2,3,4,5,6,7]>>> a[6:1:-2[7, 5, 3]>>>

When the third position is negative, take the first two opposite numbers, that is, take 1 to 6 bits, but because 6 is closed, 1 is open, so the result is [3,4,5,6,7], and then again [:: 2], the result is [7,5,3]

The rest will not be discussed.

Python: Slice character