Python--day19--collections module

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Explanation of each module of common module 1:

The file name should not be the same as the module name: (the module itself is a py file)

collection module:

namedtuple method:

Example 1:

 Example 2:

dequeue method: double-ended queue

Ordered Dictionary OrderedDict:

defaultdict default dictionary:

 1 values = [11, 22, 33,44,55,66,77,88,99,90]
 2 
 3 my_dict = {}
 4 
 5 for value in  values:
 6     if value>66:
 7         if my_dict.has_key('k1'):
 8             my_dict['k1'].append(value)
 9         else:
10             my_dict['k1'] = [value]
11     else:
12         if my_dict.has_key('k2'):
13             my_dict['k2'].append(value)
14         else:
15             my_dict['k2'] = [value]
native code 
 1 from collections import defaultdict
 2 
 3 values = [11, 22, 33,44,55,66,77,88,99,90]
 4 
 5 my_dict = defaultdict(list)
 6 
 7 for value in  values:
 8     if value>66:
 9         my_dict['k1'].append(value)
10     else:
11         my_dict['k2'].append(value)
defaultdict dictionary solution

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

1 >>> from collections import defaultdict
 2 >>> dd = defaultdict( lambda : ' N/A ' )
 3 >>> dd[ ' key1 ' ] = ' abc ' 
4 >>> dd[ ' key1 ' ] # key1 exists 
5  ' abc ' 
6 >>> dd[ ' key2 ' ] # key2 does not exist, return default value 
7  ' N/A '
Example 2

Counter method: count

Queue: queue FIFO (no index)