OrderedDict in Python



Key-value pairs will be saved in dictionaries, that are dependable knowledge buildings. Atypical dictionaries, nonetheless, didn’t protect the order of things as they have been launched earlier than to model 3.7. That is the use case for OrderedDict. A dictionary subclass referred to as OrderedDict retains observe of the order wherein keys are added. This text will go into nice element on OrderedDict, together with its options, purposes, and variations from commonplace dictionaries.

OrderedDict in : Maintaining Order in Your Dictionary


  • Acknowledge the idea behind and performance of Python’s OrderedDict.
  • Purchase the understanding wanted to create and work with OrderedDict objects.
  • Verify the primary traits that set OrderedDict other than typical dictionaries.
  • Analyse helpful purposes of OrderedDict in real-world contexts.
  • In Python 3.7+, evaluate OrderedDict with regular dictionaries.

What’s OrderedDict?

An ordered dictionary is offered within the collections module through the OrderedDict class. It retains the weather within the order that they have been initially put. This may be particularly useful in case your software’s elemental order is vital.

Let’s begin with a primary instance:

from collections import OrderedDict

# Creating an OrderedDict
od = OrderedDict()
od['apple'] = 1
od['banana'] = 2
od['cherry'] = 3


OrderedDict([('apple', 1), ('banana', 2), ('cherry', 3)])

Creating an OrderedDict

There are a number of methods to create an OrderedDict:

from collections import OrderedDict
# Methodology 1: Creating an empty OrderedDict and including objects
od1 = OrderedDict()
od1['a'] = 1
od1['b'] = 2

# Methodology 2: Creating from a listing of tuples
od2 = OrderedDict([('x', 10), ('y', 20), ('z', 30)])

# Methodology 3: Creating from one other dictionary
regular_dict = {'p': 100, 'q': 200, 'r': 300}
od3 = OrderedDict(regular_dict)

print("od1:", od1)
print("od2:", od2)
print("od3:", od3)


#od1: OrderedDict([('a', 1), ('b', 2)])
#od2: OrderedDict([('x', 10), ('y', 20), ('z', 30)])
#od3: OrderedDict([('p', 100), ('q', 200), ('r', 300)])

Key Options of OrderedDict

Allow us to now discover key options of OrderedDict with instance.

Sustaining Insertion Order

Essentially the most important characteristic of OrderedDict is its capacity to take care of the order of insertion.

od = OrderedDict()
od['first'] = 1
od['second'] = 2
od['third'] = 3

for key, worth in od.objects():
    print(f"{key}: {worth}")


#first: 1
#second: 2
#third: 3


OrderedDict offers strategies to maneuver objects to the start or finish of the dictionary.

od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])
print("Authentic:", od)

# Transfer 'c' to the start
od.move_to_end('c', final=False)
print("After transferring 'c' to the start:", od)

# Transfer 'a' to the top
print("After transferring 'a' to the top:", od)

Output :

#Authentic: OrderedDict([('a', 1), ('b', 2), ('c', 3)])
#After transferring 'c' to the start: OrderedDict([('c', 3), ('a', 1), ('b', 2)])
#After transferring 'a' to the top: OrderedDict([('c', 3), ('b', 2), ('a', 1)])

Equality Comparability

OrderedDict considers the order when evaluating for equality.

od1 = OrderedDict([('a', 1), ('b', 2)])
od2 = OrderedDict([('b', 2), ('a', 1)])
regular_dict1 = {'a': 1, 'b': 2}
regular_dict2 = {'b': 2, 'a': 1}

print("od1 == od2:", od1 == od2)
print("regular_dict1 == regular_dict2:", regular_dict1 == regular_dict2)

Output : 

#od1 == od2: False
#regular_dict1 == regular_dict2: True

Use Circumstances for OrderedDict

Allow us to now discover use circumstances of OrderedDict.

LRU (Least Just lately Used) Cache

OrderedDict is ideal for implementing an LRU cache.

from collections import OrderedDict

class LRUCache:
    def __init__(self, capability):
        self.cache = OrderedDict()
        self.capability = capability

    def get(self, key):
        if key not in self.cache:
            return -1
        return self.cache[key]

    def put(self, key, worth):
        if key in self.cache:
        self.cache[key] = worth
        if len(self.cache) > self.capability:

# Utilization
lru = LRUCache(3)
lru.put(1, 1)
lru.put(2, 2)
lru.put(3, 3)
lru.put(4, 4)  # It will take away the least lately used merchandise (1)


#OrderedDict([(1, 1), (2, 2), (3, 3)])
#OrderedDict([(2, 2), (3, 3), (4, 4)])

Sustaining Order in JSON

When working with JSON knowledge the place order issues, OrderedDict will be helpful.

import json
from collections import OrderedDict

knowledge = OrderedDict([
    ("name", "John Doe"),
    ("age", 30),
    ("city", "New York")

json_str = json.dumps(knowledge)
print("JSON string:", json_str)

# Parsing again to OrderedDict
parsed_data = json.hundreds(json_str, object_pairs_hook=OrderedDict)
print("Parsed knowledge:", parsed_data)


#JSON string: {"title": "John Doe", "age": 30, "metropolis": "New York"}

#Parsed knowledge: OrderedDict([('name', 'John Doe'), ('age', 30), ('city', 'New York')])

OrderedDict vs. Common Dict ( 3.7+)

Since  3.7, common dictionaries additionally keep insertion order. Nonetheless, there are nonetheless some variations:

# Common dict in  3.7+
regular_dict = {}
regular_dict['a'] = 1
regular_dict['b'] = 2
regular_dict['c'] = 3

# OrderedDict
from collections import OrderedDict
od = OrderedDict()
od['a'] = 1
od['b'] = 2
od['c'] = 3

print("Common dict:", regular_dict)
print("OrderedDict:", od)

# Equality comparability
print("regular_dict == od:", regular_dict == od)
print("sort(regular_dict) == sort(od):", sort(regular_dict) == sort(od))


Common dict: {‘a’: 1, ‘b’: 2, ‘c’: 3}
OrderedDict: OrderedDict([(‘a’, 1), (‘b’, 2), (‘c’, 3)])
regular_dict == od: True
sort(regular_dict) == sort(od): False

Whereas each keep order, OrderedDict offers extra strategies like `move_to_end()` and considers order in equality comparisons.


One efficient device for conserving dictionary objects of their right order is OrderedDict. Even when commonplace dictionaries in 3.7+ additionally preserve issues organised, OrderedDict nonetheless has particular capabilities that turn out to be useful typically. You could write more practical and organised code by figuring out when and how one can utilise OrderedDict, significantly when working with order-sensitive knowledge or setting up specialised knowledge buildings like LRU caches.

Continuously Requested Questions

Q1. What’s the predominant distinction between OrderedDict and an everyday dictionary in Python?

A. The principle distinction is that OrderedDict ensures the order of merchandise insertion and offers extra strategies like move_to_end(). In Python variations prior to three.7, common dictionaries didn’t keep order.

Q2. When ought to I exploit OrderedDict as a substitute of an everyday dictionary?

A. Use OrderedDict when the order of things is essential to your software, once you want operations like transferring objects to the start or finish, or when implementing order-sensitive knowledge buildings like LRU caches.

Q3. Does OrderedDict have any efficiency drawbacks in comparison with common dictionaries?

A. OrderedDict could have barely larger reminiscence utilization and will be marginally slower for sure operations as a result of sustaining order. Nonetheless, for many purposes, the distinction is negligible.

This autumn. Can I convert an everyday dictionary to an OrderedDict?

A. Sure, you may create an OrderedDict from an everyday dictionary utilizing OrderedDict(regular_dict). Nonetheless, if the unique dictionary is unordered (Python < 3.7), the ensuing OrderedDict’s order could not match the insertion order. 

Q5. Can I exploit OrderedDict with JSON in Python?

A. Sure, you should utilize OrderedDict with JSON by utilizing the object_pairs_hook parameter in json.hundreds() to parse JSON into an OrderedDict, sustaining the order of keys.