Is a Python Dictionary Ordered by Insertion (Append) Order?

Yes, starting with Python 3.7, dictionaries are guaranteed to be ordered by insertion order. This means that when you iterate over a dictionary, the items will be returned in the order they were originally inserted.

Before Python 3.7, the order of items in a dictionary was arbitrary and unpredictable. If you needed ordered behavior in earlier versions, you would typically use collections.OrderedDict.

Here's a simple example to illustrate this:

my_dict = {}
my_dict['apple'] = 1
my_dict['banana'] = 2
my_dict['cherry'] = 3

for key, value in my_dict.items():
    print(key, value)

In Python 3.7 and later, this code will always print:

apple 1
banana 2
cherry 3

However, it's important to note the following:

1. Python 3.6: In Python 3.6, dictionaries preserve insertion order as an implementation detail, but this behavior was not guaranteed by the language specification. You should not rely on it for 3.6.

2. Inheritance from dict: If you inherit from the built-in dict class and override methods, be aware that the ordering might be affected depending on how you manipulate the dictionary.

3. Collections.OrderedDict: If you need to maintain compatibility with older Python versions (older than 3.7) or require specialized ordering behavior, consider using collections.OrderedDict.

Here's an example using collections.OrderedDict:

from collections import OrderedDict

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

for key, value in ordered_dict.items():
    print(key, value)

In summary, Python dictionaries in version 3.7 and later are ordered by insertion order, providing a more predictable and convenient way to work with key-value pairs. However, remember that for older versions, collections.OrderedDict remains a reliable solution.

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