How to Use OrderedDict in Python: Syntax and Examples

Use OrderedDict from the collections module to create dictionaries that remember the order items were added. Import it with from collections import OrderedDict, then create an ordered dictionary like od = OrderedDict() and add items as usual.

Syntax

The OrderedDict is imported from the collections module. You create an ordered dictionary by calling OrderedDict(). You can add items using assignment like a normal dictionary. The order of keys is preserved in the order you add them.

python

from collections import OrderedDict

# Create an empty OrderedDict
od = OrderedDict()

# Add items
od['apple'] = 1
od['banana'] = 2
od['cherry'] = 3

Example

This example shows how OrderedDict keeps the order of items when iterating, unlike a regular dictionary in older Python versions.

python

from collections import OrderedDict

# Create an OrderedDict with some items
fruits = OrderedDict()
fruits['apple'] = 3
fruits['banana'] = 1
fruits['cherry'] = 2

# Print items in order
for fruit, count in fruits.items():
    print(f"{fruit}: {count}")

Output

apple: 3
banana: 1
cherry: 2

Common Pitfalls

One common mistake is expecting OrderedDict to sort items automatically. It only remembers the order you add items, it does not sort them. Also, in Python 3.7 and later, regular dictionaries keep insertion order, so OrderedDict is mainly useful for older versions or special methods like move_to_end().

python

from collections import OrderedDict

# Wrong: expecting automatic sorting
od = OrderedDict()
od['banana'] = 2
od['apple'] = 1
od['cherry'] = 3

# This will print in insertion order, not sorted order
for key in od:
    print(key)

# Right: use sorted() if you want sorted keys
for key in sorted(od):
    print(key)

Output

banana
apple
cherry
apple
banana
cherry

Quick Reference

Method	Description
OrderedDict()	Create a new ordered dictionary
od[key] = value	Add or update an item
od.items()	Get items in insertion order
od.move_to_end(key)	Move an existing key to the end
od.popitem(last=True)	Remove and return last or first item

Key Takeaways

OrderedDict keeps the order items are added, unlike older dicts.

Import OrderedDict from collections with: from collections import OrderedDict.

OrderedDict does not sort items automatically; use sorted() for sorting.

In Python 3.7+, regular dicts keep insertion order, so OrderedDict is less needed.

Use methods like move_to_end() for special order manipulations.