Reference · Lists

reverse

reverse(list | str) -> list | str

What it does

A list with its items in the opposite order, or a string with its characters in the opposite order. The value given is left as it was.

Examples

print(reverse([1, 2, 3]))print(reverse("hello"))print(reverse(sort([3, 1, 2])))

[3, 2, 1]olleh[3, 2, 1]

Edge cases

• An empty list gives [] and the empty string gives "".
• A string is reversed by character, not by byte, so accented letters and emoji stay whole.
• Only a list or a string: unlike most list functions, null is not taken as an empty list (see Errors).
• The list given is not changed; reverse builds a new one.

print(reverse([]), len(reverse("")))print(reverse("añb"), reverse("🙂ab"))let xs = [1, 2, 3]let r = reverse(xs)print(xs, r)

[] 0bña ba🙂[1, 2, 3] [3, 2, 1]

Errors

An argument that is not a list or a string is a runtime error, not an error value, and that includes null. Give an empty list with ?? [] first when the value may be null.

print(reverse(null))

line 1: `reverse` expects a list or str, got null

print(reverse(42))

line 1: `reverse` expects a list or str, got int

Chaining

In a pipeline reverse takes the value and needs no arguments. It is how a sort is made descending.

print([3, 1, 2] | sort | reverse)print("hello" | reverse | upper)print(["a", "b", "c"] | reverse | join(""))

[3, 2, 1]OLLEHcba

See also

sort, sort_by, first, last, slice

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