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I would like to check if a collection that has been passed to a function is ordered, that is, the order of elements is fixed. (I am not talking about "sorted".)
set is not ordered.lists and tuples are ordered.Is there a generic test that I can use?
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Yes, the order of elements in a python list is persistent. Show activity on this post. A list is a collection of elements that can contain duplicate elements and has a defined order that generally does not change unless explicitly made to do so.
The list. sort() method sorts the elements of a list in ascending or descending order using the default < comparisons operator between items. Use the key parameter to pass the function name to be used for comparison instead of the default < operator.
Definition and Usage. The sorted() function returns a sorted list of the specified iterable object. You can specify ascending or descending order. Strings are sorted alphabetically, and numbers are sorted numerically.
Ordered non-mapping collections typically implement the sequence protocol (which is mainly characterized by providing indexed access via a __getitem__ method) and can be type-tested against collections.abc.Sequence:
from collections.abc import Sequence
isinstance(set(), Sequence)
# False
isinstance(list(), Sequence)
# True
isinstance(tuple(), Sequence)
# True
If one were to insist that ordered mappings should be included, i.e. that a dict (ordered as of Python 3.7), you could test against collections.abc.Reversible:
isinstance(set(), Reversible)
# False
isinstance(list(), Reversible)
# True
isinstance(tuple(), Reversible)
# True
isinstance(dict(), Reversible)
# True
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