list_a = [1,2,3,4,5,6,7,8,9]
a,b,c,d,e,f,g,h,i = list_a
print(a,b,c,d,e,f,g,h,i)
#Receive with an equal number of parameters


_,b,c,d,e,f,g,h,_ = list_a 
print(b,c,d,e,f,g,h)
#Do not use a useless variable to receive data

Implement with * XXX

list_a = range(20)
first,*middle,last = list_a
print(first,middle,last)
#Use*To receive any number, or even none, and return one list

#A better application when there is a marker in a meta-ancestor
records = [
    ("foo",1,2),
    ("bar","hello"),
    ("foo",3,4)
]

def do_foo(x,y):
    print("foo",x,y)

def do_bar(s):
    print("bar",s)

for tags,*args in records:
    if tags == "foo":
        do_foo(*args)
    elif tags == "bar":
        do_bar(*args)

collections.deque()

import collections

#Use collections.deque(maxlen=5)To define a fixed length list,If new data has been written when it has been reached maxlen，Automatic deletion of the earliest inserted data
def search(lines,pattern,history = 5):
    previous_lines = collections.deque(maxlen=history)
    for line in lines:
        if pattern in line:
            yield line,previous_lines
        previous_lines.append(line)

if __name__ =="__main__":
    with open("test.txt","r",encoding="utf8") as f:
        for line,previous in search(f,"python",5):
            for pline in previous:
                print(pline,end="")
            print(line,end="")
            print("-"*20)

#collections.deque Introduction to Use
#A more powerful list

queue = collections.deque(["jiao","li",'hao',"yu"])
queue.appendleft("wu")
print(queue)
queue.append("haha")
print(queue)
queue.popleft()
print(queue)
print(queue[4])

heapq.nlargest(),heapq.nsmallest()

import heapq

nums = [5,56,7,6,34,2,5,7,6,89,80,-90,0,9,-67,5,45,]

print(min(nums))
print(max(nums))

print(heapq.nlargest(3,nums))
print(heapq.nsmallest(3,nums))

#Support for more complex data structures

portfolio = [
    {"name":"jiao","age":24},
    {"name":"jsdfo","age":2},
    {"name":"jisd","age":12},
    {"name":"jdo","age":36},
    {"name":"li","age":25},
    {"name":"jgd","age":50},
]

print(heapq.nlargest(3,portfolio,key=lambda s:s['age']))
print(max(portfolio,key=lambda s:s['age']))

heapq.heappush(),heapq.heappop()

import heapq


#A tuple is actually stored in the list.-priority,self._index,item)
class PriorityQueue:
    def __init__(self):
        self._queue = []
        self._index = 0

    def push(self,item,priority):
        heapq.heappush(self._queue,(-priority,self._index,item))
        self._index += 1

    def pop(self):
        return heapq.heappop(self._queue)[-1]

    def get(self):
        return self._queue

q = PriorityQueue()
q.push("foo",2)
q.push("sdf",3)
q.push("sfasc",5)
q.push("fdsg",4)
print(q.pop())
print(q.get())

collections.defaultdict(list),collections.defaultdict(set)

import collections

d = collections.defaultdict(list)#Automatic initialization without judging whether it exists
d["a"].append(1)
d["a"].append(1)
d["a"].append(1)
d["a"].append(1)
print(d['a'])

collections.OrderedDict()

import collections

d = collections.OrderedDict()#Big data shouldn't be used twice as much as regular Dictionaries
d['foo'] = 1
d["bar"] = 2
d["spam"] = 3
d["gork"] = 4
for i in d:
    print(i)

zip(),min(),sorted().max()

#Dictionaries are used for size operations. key Values are compared in size, and we generally want to use value Value comparison, but also want to get the value of key

prices = {
    "ACME":23,
    "AAPL":345,
    "IBM":34,
    "FB":24
}

#utilize zip,zip Returns an iterator that can only be used once

min_price = min(zip(prices.values(),prices.keys()))
print(min_price)

#sort
price_sorted = sorted(zip(prices.values(),prices.keys()))
print(price_sorted)

a = {
    "x":2,
    "y":5,
    "z":7
}

b = {
    "x":2,
    "y":8,
    "w":4
}

print(a.keys() & b.keys())#Look for the same key
print(a.keys() - b.keys())#Seek a There are b None of them. key
print(a.items() & b.items())#Find the same item

def dedupe(items,key = None):
    seen = set()
    for item in items:
        val = item if key is None else key(item)
        if val not in seen:
            yield item
            seen.add(val)