Python9-module1-day19

Posted on by Admin 
In addition to the built-in data types (dict, list, set, tuple), the collections module also provides several additional data types: Counter, deque, defaultdict, namedtuple, and OrderedDict, etc. 
1.namedtuple: Generate a tuple that can access element content by name 
2.deque: Double-ended queue, which can quickly append and push objects from the other side 
3.Counter: Counter, mainly used to count 
4.OrderedDict: Ordered dictionary 
5. defaultdict: a dictionary with default values

namedtuple

from collections import namedtuple
Point = namedtuple('point',['x','y','z'])
p1 = Point(3,2,1)
p2 = Point(1,2,3)
print(p1.x)
print(p1.y)
print(p1)
print(p2.x)
print(p2.y)
print(p2)
Card = namedtuple('card',['suits','number'])
c1 = Card('红心',2)
print(c1)
print(c1.number)
print(c1.suits)

about

from collections import deque
dq = and ([1,2 ])
dq .append( ' a ' )   #Put the data from the back [1,2,'a'] 
dq .appendleft( ' b ' )    #Put the data from the front ['b',1,2,'a'] 
dq. insert(2,3)      # ['b',1,3,2,'a'] 
print (dq.pop()) #Get        data from the back 
print (dq .popleft()) #Get   data from the front


a
b

# OrderedDict

from collections import OrderedDict
d = dict([( ' a ' , 1), ( ' b ' , 2), ( ' c ' , 3 )])
 # dict's Key is unordered {'a': 1, 'c': 3 , 'b': 2} 
od = OrderedDict([( ' a ' , 1), ( ' b ' , 2), ( ' c ' , 3 )])
 print (od)
 # OrderedDict's Key is an ordered 

OrderedDict ([( ' a ' , 1), ( ' b ' , 2), ( ' c ' ,3)])

# defaultdict

from collections import defaultdict
values = [11, 22, 33,44,55,66,77,88,99,90]
my_dict = defaultdict(list)
for value in  values:
    if value>66:
        my_dict['k1'].append(value)
    else:
        my_dict['k2'].append(value)

When used , if the referenced Key does not exist, it will be thrown . If you want to return a default value when the key does not exist, you can use :dictKeyErrordefaultdict

>>> from collections import defaultdict
 >>> dd = defaultdict( lambda : ' N/A ' )
 >>> dd[ ' key1 ' ] = ' abc ' 
>>> dd[ ' key1 ' ] # key1 exists 
' abc ' 
>>> dd[ ' key2 ' ] # key2 does not exist, return the default value 
' N/A '