OrderedDict (Python 2.x Backport)

1.1 · abandoned · verified Thu Apr 16

The 'ordereddict' library provides a backport of the `collections.OrderedDict` class, originally introduced in Python 2.7 and 3.1, for use in older Python 2.x environments (specifically Python 2.4, 2.5, and 2.6). It enables maintaining the insertion order of keys in a dictionary-like structure. This package is no longer maintained and serves only historical compatibility purposes for very old Python 2 projects.

Common errors

```
ImportError: No module named ordereddict
```
cause Attempting to import `ordereddict` in a Python 3.x environment or a Python 2.x environment where the package was not installed, or using the wrong import for `collections.OrderedDict`.

fix For Python 2.4-2.6, ensure `pip install ordereddict` is run. For Python 2.7+ or 3.x, use `from collections import OrderedDict`.
```
AttributeError: 'dict' object has no attribute 'items' (or similar methods maintaining order)
```
cause Attempting to iterate over a standard `dict` in insertion order in Python versions older than 3.7, or treating a `dict` as an `OrderedDict`.

fix In Python 2.4-2.6, use `from ordereddict import OrderedDict` and explicitly create an `OrderedDict` if insertion order is critical. In Python 2.7-3.6, use `from collections import OrderedDict`. In Python 3.7+, a standard `dict` maintains insertion order.

Warnings

breaking This 'ordereddict' library is obsolete for modern Python versions. `collections.OrderedDict` is built into Python 2.7, Python 3.1, and later. Furthermore, standard Python dictionaries (`dict`) guarantee insertion order since Python 3.7.
Fix: For Python 2.7+, use `from collections import OrderedDict`. For Python 3.7+, a regular `dict` maintains insertion order, so `OrderedDict` might only be needed for specific API compatibility or advanced features like `move_to_end` or order-sensitive equality comparisons.
gotcha The performance characteristics of this Python-based backport `ordereddict.OrderedDict` may differ significantly from the C-optimized `collections.OrderedDict` in newer Python versions.
Fix: Avoid using this backport unless strictly required for compatibility with Python 2.4-2.6. Prioritize `collections.OrderedDict` or standard `dict` where possible.

Install

pip install ordereddict Install for Python 2.x

Imports

OrderedDict
wrong:
```
from collections import OrderedDict
```
correct:
```
from ordereddict import OrderedDict
```
The 'collections' module import is for Python 2.7+ and 3.x. This package provides the 'ordereddict' module for older Python 2 versions.

Quickstart

Demonstrates importing and using the `OrderedDict` class from the backport for Python 2.4-2.6. It includes a version check to highlight the library's specific compatibility window.

import sys

# This library is for Python 2.x <= 2.6
# For Python 2.7+ or 3.x, use 'from collections import OrderedDict'

if sys.version_info < (2, 7) and sys.version_info >= (2, 4):
    from ordereddict import OrderedDict
    print("Using ordereddict backport")
    od = OrderedDict()
    od['first'] = 1
    od['second'] = 2
    od['third'] = 3
    print(od.items())
else:
    print("This library is not needed for your Python version.")
    print("Use 'from collections import OrderedDict' instead.")

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