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 python dictionary orderdict

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An OrderedDict is a dictionary subclass that remembers the order that keys were first inserted. The only difference between dict() and OrderedDict() is that:

Python - dict

OrderedDict preserves the order in which the keys are inserted. A regular dict doesn’t track the insertion order, and iterating it gives the values in an arbitrary order. By contrast, the order the items are inserted is remembered by OrderedDict.

python - Sample - python code :

# A Python program to demonstrate working of OrderedDict
from collections import OrderedDict
 
print("This is a Dict:\n")
d = {}
d['a'] = 1
d['b'] = 2
d['c'] = 3
d['d'] = 4
 
for key, value in d.items():
    print(key, value)
 
print("\nThis is an Ordered Dict:\n")
od = OrderedDict()
od['a'] = 1
od['b'] = 2
od['c'] = 3
od['d'] = 4
 
for key, value in od.items():
    print(key, value)

python tutorial - Output :

This is a Dict:
('a', 1)
('c', 3)
('b', 2)
('d', 4)

This is an Ordered Dict:
('a', 1)
('b', 2)
('c', 3)
('d', 4)

Important Points:

  1. Key value Change: If the value of a certain key is changed, the position of the key remains unchanged in OrderedDict.

python - Sample - python code :

# A Python program to demonstrate working of key 
# value change in OrderedDict
from collections import OrderedDict
 
print("Before:\n")
od = OrderedDict()
od['a'] = 1
od['b'] = 2
od['c'] = 3
od['d'] = 4
for key, value in od.items():
    print(key, value)
 
print("\nAfter:\n")
od['c'] = 5
for key, value in od.items():
    print(key, value)

python tutorial - Output :

Before:

('a', 1)
('b', 2)
('c', 3)
('d', 4)

After:

('a', 1)
('b', 2)
('c', 5)
('d', 4)

  1. Deletion and Re-Inserting: Deleting and re-inserting the same key will push it to the back as OrderedDict however maintains the order of insertion.

python - Sample - python code :

# A Python program to demonstrate working of deletion 
# re-inserion in OrderedDict
from collections import OrderedDict
 
print("Before deleting:\n")
od = OrderedDict()
od['a'] = 1
od['b'] = 2
od['c'] = 3
od['d'] = 4
 
for key, value in od.items():
    print(key, value)
 
print("\nAfter deleting:\n")
od.pop('c')
for key, value in od.items():
    print(key, value)
 
print("\nAfter re-inserting:\n")
od['c'] = 3
for key, value in od.items():
    print(key, value)

python tutorial - Output :

Before deleting:

('a', 1)
('b', 2)
('c', 3)
('d', 4)

After deleting:

('a', 1)
('b', 2)
('d', 4)

After re-inserting:

('a', 1)
('b', 2)
('d', 4)
('c', 3)


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