Python Learning Notes (10)-Advanced features

One, slice

1. Definition:

It is often tedious to take an operation with a specified index range, so Python provides a slice (Slice) operator.

2. Syntax:

A[1:3]          Remove 1 to 3, is a positive case, the missing fill is 0 (first), End (the last) B[-3:] Take the third to the bottom of the penultimate, is negative, the absence of           filling is 1 (last) C[1:10:2]     From 1 to 10, each of 2 takes one

The same syntax as MATLAB, that is, a vector can be a matrix operation. Can be used for list.tuple,string,dict,set, etc.

Second, slicing

1. Definition:

Given a list or tuple, we can iterate through for the list or tuple through a loop, which we call an iteration (iteration).

2, Python Iteration special point:

Python has a more for circular abstraction than the Java for Loop, because the Python for loop can be used not only on a list or a tuple, but also on other objects that can iterate. List this data type although there is subscript, but many other data types are not subscript, but as long as the object can be iterated, whether or not subscript, can iterate, such as dict can iterate:

>>> d = {' A ': 1, ' B ': 2, ' C ': 3}>>> for key in D: ...     Print (key) ... ACB

since dict are not ordered sequentially, the resulting iterations may differ in order.

3, Dict iterative attention points:

(1) can be iterated by key (default), as above

(2) You can also iterate by value

For value in D.values ()

(3) You can also iterate both (Python special point)

For K, V in D.items ()

4, how to determine whether the iteration: using the Collections Module Iterable type to judge

>>> from Collections Import iterable>>> isinstance (' abc ', iterable) # Whether STR can iterate true>>> Isinstance ([i], iterable) # Whether the list can iterate true>>> isinstance (123, iterable) # integer can be iterated false

　　

5, how to implement the C language subscript implementation: Python built-in enumerate functions can change a list into an index-element pair

>>> for I, value in enumerate ([' A ', ' B ', ' C ']):     ... Print (i, value) ... 0 A1 B2 C

　　

Python Learning Notes (10)-Advanced features