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Why don't tuples in Python have a sort method?

·513 words·3 mins·
AJ
Author
AJ

My friend James from Don’t Use This Code gave a teaser the other day:

Why can’t you .sort a tuple? Why doesn’t the method exist?

My answer below.

We can use sorted on a tuple.
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Let’s quickly review what sorted does:

>>> help(sorted)
Help on built-in function sorted in module builtins:

sorted(iterable, /, *, key=None, reverse=False)
    Return a new list containing all items from the iterable in ascending order.

    A custom key function can be supplied to customize the sort order, and the
    reverse flag can be set to request the result in descending order.

So you are right, but we’ll get a list back not a tuple.

Let’s keep going.

What is a tuple anyway?
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According to the Python documentation, a tuple is a builtin immutable sequence that is typically used to store collections of heterogeneous data, and then it gives the example of enumerate().

The key phrase here is “heterogeneous data”, meaning it is not a collection the same way a list is.

Let’s look at the example of enumerate() by using it in action:

alphabet = [chr(i) for i in range(65, 91)]
# alphabet = ['A', 'B', 'C', 'D', 'E', 'F', ...]
enumerated_alphabet = [pair for pair in enumerate(alphabet)]
# enumerated_alphabet = [(0, 'A'), (1, 'B'), (2, 'C'), ...]

We just used enumerate() to give us a list of tuple[int, str]. Integers and strings are not the same data-type. This pairing is exactly an example of the use-case given by the documentation. A tuple is typically a “pairing” of items. You can’t sort a tuple because you aren’t meant to sort pairs of data, only retrieve them by index, or by unpacking them via iterable unpacking.

If we further explore tuple, we find there is also namedtuple, for when we want to access data by name instead of index. Further, if we look at the Python DB-API Spec, PEP-249, all the functions for retrieving data return…

(e.g. a list of tuples)

So we find that tuples are immutable because they represent a pairing of data which shouldn’t be modified, so think of it like a record of some kind. It doesn’t make sense to take a record and try to sort the record itself.

I think we can still use sorted on a tuple.
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You can call sorted if you want to, but let’s say we have a table, T, with columns id, and username.

If you query T and get a result, r, which is [(123, "AJ"), (456, "Arthur"), ...], it wouldn’t make sense for you to try and do something like first_element = r[0]; first_element.sort(). How would you compare an int against a str and see which one is lesser or greater?

So that’s why there is no .sort method for tuples.

Thank you for joining me in this exercise, I enjoyed it very much.

If you also found this Python exercise interesting, please visit my friends over at Don’t Use This Code on LinkedIn, they have a lot more posts like this as well as articles, videos, and webinars.

Thanks for reading.

– AJ