Data structure related modules (list)

All content referenced from Python cookbook

1. Extract sequence assignment to multiple variables in general, our assignment variables are:

a = 1

Python can do this:

a,b = 1,2

or this:

E=[1,2,3,4]a,b,c,d=e

Of course, you want to unzip a few layers to unzip a few layers, such as:

data = [' ACME ', ' 91.1 ', ']name ', ' shares ', ' Price, ' (year, Mon, day) = data

If you just want a few of these variables, this .... Python does not give a special way, you can use some of the non-trivial variable names to occupy a bit. Like what:

data = [' ACME ', ' 91.1 ', ']_ ', shares, price, _ = Data

Although the list is parsed, the same applies to strings, file objects, iterators, generators

s = ' Hello ' a,b,c,d,e = s

Sometimes the elements of an iteration object will exceed the number of variables, so what to do is to use the asterisk expression.

Record = (' Dave ', ' [email protected] ', ' 773-555-1212 ', ' 847-555-1212 ') name, email, *phone_numbers = record

The extracted phone_numbers is always a list, even if there is no element, of course, the more common is to take the asterisk expression as a parameter such as:

def add (*args): n=0 for I in Args:n+=i return n

Then we can pass any parameter to the Add function ~

Add (+/-) Add (5,1,2,6,7)

2. The most frequently occurring elements in a sequence

collections.CounterClasses are designed specifically for this type of problem, and a most_common() way to give answers directly

words = [' look ',  ' to ',  ' my ',  ' eyes ',  ' look ',  ' into ',  ' my ',  ' Eyes ', ' the ',  ' Eyes ',  ' the ',  ' Eyes ',  ' the ',  ' Eyes ',  ' not ',  ' around ',  ' The ', ' Eyes ',  ' don ' t ',  ' look ',  ' around ',  ' the ',  ' Eyes ',  ' look ',  ' into ', ' my ',   ' Eyes ',  "You ' re",  ' under ']from collections import counterword_counts =  counter (words) Top_three = word_counts.most_common (3) (Print (Top_three) # outputs [(' Eyes ',  8),  (' The ',  5),  (' Look ',  4)] 

On the underlying implementation, an Counter object is a dictionary that maps the element to the number of times it appears. Like what:

>>> word_counts[' not ']1

And you can manually increase the count

word_counts[' not ']+=1

CounterInstances can perform mathematical operations

This article is from the "mechanism of small Wind" blog, please be sure to keep this source http://xiaofengfeng.blog.51cto.com/8193303/1885778

Data structure related modules (list)