Remove Duplicates

Whiteboard: Easier
Challenge: Easier
Concepts: Lists, Sets
Download: remove-duplicates.zip
Solution: Remove Duplicates: Solution

In this challenge, you’ll write a function that is given a list of items and returns a new list of those items, in the same order, but with duplicate removed.

For example:

>>> deduped([1, 1, 1])
[1]

Keep items in the order where they first appeared:

>>> deduped([1, 2, 1, 1, 3])
[1, 2, 3]

A list with no duplicates would return the same:

>>> deduped([1, 2, 3])
[1, 2, 3]

This should return a new list, not mutate the existing list:

>>> a = [1, 2, 3]
>>> b = deduped(a)
>>> a == b
True

>>> a is b
False

An empty list should return an empty list:

>>> deduped([])
[]

We’ve given you a skeleton in remove_duplicates.py:

dedupe.py

def deduped(items):
    """Return new list from items with duplicates removed."""