How Can I Efficiently Remove Duplicates from a List While Preserving Order in Python?

Preserving Order While Removing Duplicates from a List

Removing duplicate elements from a list while maintaining the original order can be a challenge, as using a set to eliminate duplicates typically disrupts the initial sequence.

To address this issue, the Python community has developed various built-in and idiomatic solutions. One of the most efficient options is a function known as f7, which leverages a set to efficiently detect and remove duplicates:

def f7(seq):
    seen = set()
    seen_add = seen.add
    return [x for x in seq if not (x in seen or seen_add(x))]

This function employs a set named seen to swiftly identify and remove duplicates. The secret optimization lies in assigning seen.add to seen_add as a local variable. This prevents Python from dynamically resolving seen.add on each iteration, which can lead to performance degradation due to the potential for seen.add to change.

Other alternatives, such as the ordered set data structure from ActiveState, are also available if you anticipate performing frequent duplicate removal operations on the same dataset.

It's imperative to note that in the provided code, seen.add() consistently returns None, necessitating the use of the logical or operator as a method to trigger a set update.

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