How to Convert Between OrderedDict and dict in Python

This guide explains how to convert between OrderedDict (from the collections module) and regular dict objects in Python. We'll also cover converting an OrderedDict to a list. The key difference between a standard dict and an OrderedDict is that the OrderedDict remembers the insertion order of keys, whereas, before Python 3.7, regular dictionaries did not guarantee any particular order. In Python 3.7 and later, standard dict objects do preserve insertion order.

Converting OrderedDict to `dict

To convert an OrderedDict to a standard (unordered in Python < 3.7, ordered in Python >= 3.7) dictionary, simply use the dict() constructor:

from collections import OrderedDict

ordered_dict = OrderedDict(
    [('first', 'tom'),
     ('last', 'nolan'),
     ('age', 25)]
)

regular_dict = dict(ordered_dict)  # Convert to a regular dict

print(regular_dict)
# Output (Python 3.7+): {'first': 'tom', 'last': 'nolan', 'age': 25}
# Output (Python < 3.7): {'last': 'nolan', 'first': 'tom', 'age': 25} (order *might* be different)

print(type(regular_dict))  # Output: <class 'dict'>

• dict(ordered_dict): This creates a new dictionary object. The new dictionary will have the same key-value pairs as the OrderedDict, but it will be a standard dict.

If the OrderedDict is nested, the recommended way to convert it to dict is to use json.dumps and json.loads.

from collections import OrderedDict
import json

ordered_dict = OrderedDict(
  [('name', 'tomnolan'),
    ('address', OrderedDict([('post_code', 123)])),
    ]
)

json_str = json.dumps(ordered_dict)
regular_dict = json.loads(json_str)

print(regular_dict)        # Output: {'name': 'tomnolan', 'address': {'post_code': 123}}
print(type(regular_dict))  # Output: <class 'dict'>

Converting dict to OrderedDict

To convert a regular dict to an OrderedDict, pass the dictionary to the OrderedDict constructor:

from collections import OrderedDict

my_dict = {
    'first': 'tom',
    'last': 'nolan',
    'age': 25,
}

ordered_dict = OrderedDict(my_dict)  # Convert to OrderedDict
print(ordered_dict)
# Output: OrderedDict([('first', 'tom'), ('last', 'nolan'), ('age', 25)])

• OrderedDict(my_dict): This creates a new OrderedDict object, preserving the insertion order of the original dict (in Python 3.7+).

Converting OrderedDict to a List

To convert an OrderedDict to a list, you have several options, depending on what you want in the list:

• List of keys:

  list_of_keys = list(ordered_dict.keys()) # Or simply: list(ordered_dict)
  print(list_of_keys) # Output: ['name', 'age', 'topic']

• List of values:

  list_of_values = list(ordered_dict.values())
  print(list_of_values) # Output: ['tomnolan', 25, 'Python']

• List of (key, value) tuples:

  list_of_items = list(ordered_dict.items())
  print(list_of_items) # Output: [('name', 'tomnolan'), ('age', 25), ('topic', 'Python')]
  • The items() method will return a list of tuples.
  • list_of_items[0] accesses the tuple element at index 0.
  • list_of_items[0][0] and list_of_items[0][1] access the tuple elements in the list.

When to Use OrderedDict vs. dict (Python 3.7+)

• Python 3.7 and later: Standard dict objects preserve insertion order. In most cases, you don't need OrderedDict anymore. Use a regular dict unless you specifically need the extra features of OrderedDict (see below).
• Python 3.6 and earlier: dict did not guarantee order. If you need to maintain insertion order and are using an older Python version, you must use OrderedDict.
• Explicit Intent: Even in Python 3.7+, using OrderedDict can be a way to explicitly communicate to other developers (and your future self) that the order of the items is significant.
• Equality Check: OrderedDict checks for equality of contents and order, and dict only checks for equality of contents.