Python Cookbook-1-Data structures and algorithms

1 Sequence decompression: through * to pass the match

*a, B = somelist, First, *mid, last = Somelist, a, *b = Somelist

2 using bidirectional queues: From collections import deque

Q = deque (maxlen=5) can be fixed length

Q = deque () can also be any length

can be inserted and removed from both ends, append, Appendleft, pop, popleft

3 finding the largest or smallest n elements: using heapq (heap queue)

HEAPQ. nlargest (N, Alist) heapq. nsmallest (n, alist) is suitable when n is relatively small

You can also sorted (alist) [-N:] Sorted (alist) [: n] for relatively large n

4 Implementing a priority queue

Import HEAPQ class priorityqueue:     def __init__ (self):         = []        = 0    def  push (self, item, priority):        Heapq.heappush (self._ Queue, (-priority, Self._index, item        )+ = 1    def  pop (self):         return Heapq.heappop (self._queue) [-1]

5 keys in a field map multiple values Defaultdict

Defaultdict

Defaultdict(list)d[' a '].  Append(1)d[' a '].  Append(2)
d[' B '].append (5)

Python Cookbook-1-data structures and algorithms