Using a comparator function to sort

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In Python 3 there is no cmp argument for the sorted function (nor for list.sort).

According to the docs, the signature is now sorted(iterable, *, key=None, reverse=False), so you have to use a key function to do a custom sort. The docs suggest:

Use functools.cmp_to_key() to convert an old-style cmp function to a key function.

Here’s an example:

>>> def compare(x, y):
...     return x[0] - y[0]
... 
>>> data = [(4, None), (3, None), (2, None), (1, None)]
>>> from functools import cmp_to_key
>>> sorted(data, key=cmp_to_key(compare))
[(1, None), (2, None), (3, None), (4, None)]

However, your function doesn’t conform to the old cmp function protocol either, since it returns True or False. For your specific situation you can do:

>>> your_key = cmp_to_key(make_comparator(cmpValue))
>>> sorted(data, key=your_key)
[(1, None), (2, None), (3, None), (4, None)]

using the make_comparator function from @Fred Foo’s answer.

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