Double-ended queue in Python

OrderedDict is a subclass of the dict object in Python. The only difference between OrderedDict and dict is that in OrderedDict, it maintains the order of inserted keys. In a dictionary, sorting may or may not occur.

OrderedDict is a standard library class located incollectionsModule.

Firstly, we need to import it to use it.SetStandard library module.

import　collections

In this section, we will see some operations related to OrderedDict and the differences between OrderedDict and Dict.

We can put some keys and values into Dict and OrderedDict. In this example, we can see that the order of Dict may be different. However, for OrderedDict, it will be fixed.

Example Code

import　collections
#Create　normal　dict
my_dict　=　{}
my_dict['AA']　=　11
my_dict['BB']　=　22
my_dict['CC']　=　33
my_dict['DD']　=　44
for　item　in　my_dict.items():
　　　print(item)
print()
#Create　ordered　dict
my_ord_dict　=　collections.OrderedDict()
my_ord_dict['AA']　=　11
my_ord_dict['BB']　=　22
my_ord_dict['CC']　=　33
my_ord_dict['DD']　=　44
for　item　in　my_ord_dict.items():
　　　print(item)

Output Result

('AA',　11)
('CC',　33)
('BB',　22)
('DD',　44)
('AA',　11)
('BB',　22)
('CC',　33)
('DD',　44)

Change the value of a specified key

For OrderedDict, the order of keys will not change when the value of a specified key is changed. We can see that this statement may be correct or incorrect for Dict type objects.

Example Code

import　collections
#Create　normal　dict
my_dict　=　{}
my_dict['AA']　=　11
my_dict['BB']　=　22
my_dict['CC']　=　33
my_dict['DD']　=　44
for　item　in　my_dict.items():
　　　print(item)
#Change　the　value　for　key　BB
my_dict['BB']　=　100
print('After　changing　in　Dict')
for　item　in　my_dict.items():
　　　print(item)
print()
#Create　ordered　dict
my_ord_dict　=　collections.OrderedDict()
my_ord_dict['AA']　=　11
my_ord_dict['BB']　=　22
my_ord_dict['CC']　=　33
my_ord_dict['DD']　=　44
for　item　in　my_ord_dict.items():
　　　print(item)
#Change　the　value　for　key　BB
my_ord_dict['BB']　=　100
print('After　changing　in　Ordered　Dict')
for　item　in　my_ord_dict.items():
　　　print(item)

Output Result

('AA',　11)
('BB',　22)
('CC',　33)
('DD',　44)
After　changing　in　Dict
('AA',　11)
('CC',　33)
('DD',　44)
('BB',　100)
('AA',　11)
('BB',　22)
('CC',　33)
('DD',　44)
After　changing　in　Ordered　Dict
('AA',　11)
('BB',　100)
('CC',　33)
('DD',　44)

Delete and reinsert elements in OrderedDict

When an element is deleted from an OrderedDict and the key and value are reinserted, it will push it back to the end. Although it maintains the order when inserting, it will delete the ordering information and be reinserted as a new entry when deleting.

Example Code

import　collections
#Create　ordered　dict
my_ord_dict　=　collections.OrderedDict()
my_ord_dict['AA']　=　11
my_ord_dict['BB']　=　22
my_ord_dict['CC']　=　33
my_ord_dict['DD']　=　44
for　item　in　my_ord_dict.items():
　　　print(item)
#Delete　item　in　key　BB
my_ord_dict.pop('BB')
print('After　Deleting')
for　item　in　my_ord_dict.items():
　　　print(item)
#re-inserting　item　
my_ord_dict['BB']　=　22
print('After　Re-inserting')
for　item　in　my_ord_dict.items():
　　　print(item)

Output Result

('AA',　11)
('BB',　22)
('CC',　33)
('DD',　44)
After　Deleting
('AA',　11)
('CC',　33)
('DD',　44)
After　Re-inserting
('AA',　11)
('CC',　33)
('DD',　44)
('BB',　22)