Python basic content: collections module

collections is a built-in collection module in Python that provides many useful collection classes. 1.Counter Counter is a simple counter, for example, counting the number of characters appearing: >>> import
collections>>> obj =
collections.Counter('applebanana')> ;>> print(obj)Counter({'a': 4, 'n':
2, 'p': 2, 'e': 1, 'l': 1, 'b': 1 }) 2.OrderedDict ordered dictionary When using dict, the Key is unordered. When iterating over dict, we cannot determine the order of Keys. If you want to maintain the order of Keys, you can use OrderedDict:>>> od =
collections.OrderedDict()>>> od['k2']
='k2'>> > od['k1'] =
'k1'>>> odOrderedDict([('k2',
'k2'), ('k1', 'k1')]) or> ;>> od =
collections.OrderedDict([('k2','v2'),('k1','v1')])>>> odOrderedDict([('k2',
'v2'), ('k1', 'v1')]) 3.defaultdict The default dictionary will set a default type for the dictionary value import collectionsnum =
[11,22,33,44, 55,66,77,88,99] #Add the default list type my_dic for the value of the my_dic dictionary =
collections.defaultdict(list) for i in num: if i > 66: my_dic['k1'].append (i) else: my_dic['k2'].append(i)print(my_dic) 4.namedtuple Named Tuple Namedtuple is a function that is used to create a custom tuple object and specifies the number of tuple elements. , and can use attributes instead of indexes to reference an element of the tuple. In this way, we can easily define a data type using namedtuple, which has the invariance of tuple and can be referenced based on attributes. It is very convenient to use>>>person = collections.namedtuple('pp', ['name','age'])>>>p = person('apple',2)>>>print(p.name)>>>print(p.age) 5.deque two-way queue When using a list to store data, accessing elements by index is very fast, but inserting and deleting elements is very slow, because the list is linear storage, and when the amount of data is large, the efficiency of insertion and deletion is very low. Deque is a two-way list for efficient implementation of insertion and deletion operations, suitable for queues and stacks:>>> dli =
collections.deque([1,2,3])>>>
dli.append(4)>>> dlideque([1, 2, 3, 4])>>>
dli.appendleft(5) #appendleft insert data to the left>> ;> dlideque([5, 1, 2, 3, 4]) 6.queue single-item queue (in the queue module) import queueq = queue.Queue()q.put(123)q.put(456)print(q .qsize())print(q.get())#q.get() will take out the data in the single item queue in sequence print(q.get())

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