Python Simple data structure (i)

Study Notes

#python 3.5.2

Extract sequence assignment to multiple variables

>>> x= (a,b,c=x>>>) >>> a1>>> b2>>> c3>>> data=[' 1 ', ' 2 ', ' 3 ', ' 4 ', ' 5 ']>>> _,a,_,_,b=data>>> a ' 2 ' >>> B ' 5 ' >>> y= (3,4) >>> a,b,c=  Ytraceback (most recent): File "<pyshell#14>", line 1, <module> a,b,c=yvalueerror:not enough Values to unpack (expected 3, got 2) >>> >>> data=[' 1 ', 2, (3,4),5]>>> a,b,l,c=data>>> L (3, 4) >>> a ' 1 ' >>> c5>>>

Unzip an iterative object to assign values to multiple variables

>>> l=[1,2,3,4,5,6]>>> head,*tail=l>>> head1>>> tail[2, 3, 4, 5, 6]>>> Head,*middle,tail=l>>> head1>>> middle[2, 3, 4, 5]>>> tail6>>> L=[' aaa ', 10, (all ), ' dddd ']>>> head,*middle,tail=l>>> head ' AAA ' >>> middle[10, (1, 2, 3)]>>> tail ' dddd ' >>> name,age, (a,b,c),addr=l>>> a1>>> b2>>> c3>>> addr ' dddd ' > >> age10>>>

Keep Last n elements

>>> from Collections Import deque>>> Q=deque (maxlen=4) >>> q.append (1) >>> Q.append (2) >>> q.append (3) >>> qdeque ([1, 2, 3], maxlen=4) >>> q.append (4) >>> qdeque ([1, 2, 3 , 4], maxlen=4) >>> q.append (5) >>> Qdeque ([2, 3, 4, 5], maxlen=4) >>> q.append (6) >>> Qdeque ([3, 4, 5, 6], maxlen=4) >>> q.appendleft (0) >>> Qdeque ([0, 3, 4, 5], maxlen=4) >>> Q.appen Dleft ( -1) >>> Qdeque ([-1, 0, 3, 4], maxlen=4) >>>

Finds the largest or smallest n elements

>>> import Heapq>>> nums = [1, 8, 2, 23°c, 7, -4,,, 2]>>> heapq.nlargest (3,nums) [42 , Notoginseng, 23]>>> heapq.nlargest (4,nums) [All, Panax Notoginseng, 23]>>> heapq.nsmallest (2,nums) [ -4, 1]>>> Heapq.nsmallest (4,nums) [ -4, 1, 2, 2]>>>

Implementing a priority queue

>>> Import heapq>>> queue=[]>>> heapq.heappush (Queue, (3, ' three ')) >>> Heapq.heappush (Queue, (2, ')) >>> Heapq.heappush (Queue, (5, ' five ')) >>> Heapq.heappush (queue, (1 , ' one ') >>> Heapq.heappush (Queue, (4, ' four ')) >>> Heapq.heappop (queue) (1, ' one ') >>> Heapq.heappop (Queue) (2, ' both ') >>> Heapq.heappop (Queue) (3, ' three ') >>> Heapq.heappop (Queue) (4, ' Four ') >>> Heapq.heappop (queue) (5, ' five ') >>>

Dictionary middle key Mapping multiple values

>>> from Collections Import defaultdict>>> d=defaultdict (list) >>> d[' A '].append (1) > >> d[' A '].append (2) >>> d[' A '].append (3) >>> d[' B '].append ( -1) >>> d[' B '].append (-2) >>> d[' C '].append (' C ') >>> ddefaultdict (<class ' list '), {' B ': [-1,-2], ' C ': [' C '], ' a ': [1, 2, 3]} ) >>>

Dictionary hold Order

>>> from Collections Import ordereddict>>> d=ordereddict () >>> d[' B ']=2>>> d[' A ']= 1>>> d[' C ']=3>>> d[' F ']=6>>> d[' E ']=5>>> dordereddict ([' B ', 2), (' A ', 1), (' C ', 3) , (' F ', 6), (' E ', 5)]) >>> for I in D:print (I,d[i]) B 2A 1C 3F 6E 5>>> d=dict () >>> d[' B '] =2>>> d[' A ']=1>>> d[' C ']=3>>> d[' F ']=6>>> d[' E ']=5>>> for I in D:prin T (I,d[i]) A 1F 6C 3B 2E 5>>>

The operation of the dictionary

>>> prices = {     ' ACME ': 45.23,     ' AAPL ': 612.78,     ' IBM ': 205.55,     ' HPQ ': 37.20,      ' FB ':  10.75}>>> min_price=min (Zip (prices.values (), Prices.keys ())) >> > min_price (10.75,  ' FB ') >>> max_price=max (Zip (prices.values (), Prices.keys ())) > >> max_price (612.78,  ' AAPL ') >>> prices_sorted=sorted (Zip (prices.values (), Prices.keys ())) >>> prices_sorted[(10.75,  ' FB '),  (37.2,  ' HPQ '),  (45.23,  ' ACME '),  (205.55,  ' IBM '),  (612.78,  ' AAPL ')]>>> min (prices) ' AAPL ' >>>  max (Prices) ' IBM ' >>> min (prices,key=lambda x:prices[x]) ' FB ' >>> max ( Prices,key=lambda x:prices[x]) ' AAPL ' >>> prices[min (Prices,key=lambda x:prices[x]) 10.75>>> prices[maX (Prices,key=lambda x:prices[x])]612.78>>> 

Find the same point for two dictionaries

>>> a = {' X ': 1, ' Y ': 2, ' z ': 3}>>> b = {' W ': Ten, ' X ': one, ' y ': 2}>>> A.keys () & B.keys () {' x ', ' Y '}>>> a.keys ()-B.keys () {' Z '}>>> a.items () & B.items () {(' Y ', 2)}&G T;>>

Delete sequence of same elements and maintain order

>>> def dedupe (items): Seen =set () for item in Items:if item not in Seen:yield Itemseen.add (item) >>> a = [ 1, 5, 2, 1, 9, 1, 5, 10]>>> list (Dedupe (a)) [1, 5, 2, 9, 10]

>>>

Named slices

>>> record = ' ......... ..... 100 ..... 513.25 ... ' >>> shares=slice (20,23) >>> price=slice (31,37) >>> Cost=int (record[ Shares]) *float (Record[price]) >>> cost51325.0>>>

This article is from the "Chauncey" blog, make sure to keep this source http://cqwujiang.blog.51cto.com/10808946/1948892

Python Simple data structure (i)