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A frequently asked question is if dictionary objects are ordered. The uncertainty arises from the fact that dictionaries were not sorted in versions before Python 3/7. In Python 3/7 and all later versions, dictionaries are sorted by the order of item insertion. In our example this means the dictionary keeps the order in which we defined the dictionary.

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Shuffling a dictionary is not possible in Python. However, we can rearrange the order of keys of a dictionary.

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Python's dictionaries have no order, so indexing like you are suggesting (fruits) makes no sense as you can't retrieve the second element of something that has no order. They are merely sets of key:value pairs.

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Note that the dictionary will be sorted based on the data types it contains. Strings are sorted alphabetically whereas numbers are sorted in ascending order. If keys or values consist of different data types that have no way of being compared with one another, such as numbers and strings, your Python interpreter will raise an error.

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Python dictionary keys order

In Python versions 3/5 and earlier dictionaries cannot store items in an ordered manner like lists or tuples. However, it is possible to create a sorted representation of a dictionary.

Note that OrderedDict was introduced into the standard library in python (their website) 2/7. If you have an older version of python (more), you can find recipes for ordered dictionaries on ActiveState.

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Until recently, Python dictionaries did not preserve the order in which items were added to them. For instance, you might type {'fruits': ['apples', 'oranges'], 'vegetables': ['carrots', 'peas']} and get back {'vegetables': ['carrots', 'peas'], 'fruits': ['apples', 'oranges']}. If you wanted a dictionary that preserved order, you could use the OrderedDict class in the standard library module collections.

As of Python 3/6, dictionaries now preserves the insertion order. So using Python 3/6+, you could get the index by converting the dict_keys to a list.

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Dictionaries are unordered so you cannot reverse them. The order of the current output is arbitrary.

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Note: This function works only when the grades are arranged in descending order, and that relies on the order of the dictionary being maintained. If you’re using a version of Python older than 3/6, then you’ll need to use an OrderedDict instead.

As you can visually now see, in the original proposal, a lot of space is essentially empty to reduce collisions and make look-ups faster. With the new approach, you reduce the memory required by moving the sparseness where it's really required, in the indices.

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Before we dive in, I think it’s important to address a couple of these questions right out of the gate. First, dictionaries have a temporal ordering—at least since Python 3/7—which means that items are sorted by the order in which they were added.

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See what's new in python 3.8

This is not the case now since only the required entries are stored (those that have been inserted) and a sparse array of type intX_t (X depending on dict size) 2/3 * dk_sizes full is kept. The empty space changed from type PyDictKeyEntry to intX_t.

Speed wise, the difference isn't so drastic, there's places where the new dict might introduce slight regressions ([key-lookups, for example]) while in others (iteration and resizing come to mind) a performance boost should be present. Overall, the performance of the dictionary, especially in real-life situations, improves due to the compactness introduced.

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Remember that keys and values can be any data type, but it's rare for them to be non-primitive types. Additionally, dictionaries don't store or structure their content in any specific order. If you need an ordered sequence of items, it's best to create a list in Python, not a dictionary.

In Python 2/7, dictionaries are unordered structures. The order of the dictionaries’ items is scrambled. This means that the order of the items is deterministic and repeatable.

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IPython Assumes That dict Order Doesn’t Matter

The order keys are iterated in is arbitrary. It was only a coincidence that they were in sorted order.

Previous: Write a Python program to create an instance of an OrderedDict using a given dictionary. Sort the dictionary during the creation and print the members of the dictionary in reverse order.

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The first array, dk_entries, holds the entries (of type PyDictKeyEntry) for the dictionary in the order that they were inserted. Preserving order is achieved by this being an append only array where new items are always inserted at the end (insertion order).

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But don't want the existing way it is showing alphabetical order based on the actual key names

In current Python versions, the widely used built-in dict type doesnot specify an order for the key/value pairs stored. This makes ithard to use dictionaries as data storage for some specific use cases.

Rather, it is a MutableMapping that remembers the order of key insertion

If we want to order or sort the dictionary objects by their keys, the simplest way to do so is by Python's built-in sorted method, which will take any iterable and return a list of the values which has been sorted (in ascending order by default). There is no class method for sorting dictionaries as there is for lists, however the sorted method works the same exact way.

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In Python 3/5, dictionaries are still unordered, but this time, randomized data structures. This means that every time you re-run the dictionary, you’ll get a different items order.

You might think that this change makes the OrderedDict class obsolete. However, there are at least two good reasons to continue using OrderedDict. First, relying on standard dict objects to preserve order will cause your code to break on versions of CPython earlier than 3/5 and on some alternative implementations of Python 3/5 and 3/6. Second, using an OrderedDict communicates your intention to rely on the order of items in your dictionary being preserved, both to human readers of your code and to the third-party libraries you call within it.

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