Find Duplicates in List Python: Quick Guide

You can use the set() function and list comprehension in Python to find duplicate values in a list. Here are the specific steps:

1. Create an empty set called “duplicates” to store duplicate values.
2. Traverse each element in the list using list comprehension.
3. If the element already exists in the collection, it will be added to the duplicate list.
4. Otherwise, add the element to the collection.
5. Finally, return to the duplicate list.

Here is an example code snippet:

def find_duplicates(lst):
    duplicates = []
    seen = set()
    for item in lst:
        if item in seen:
            duplicates.append(item)
        else:
            seen.add(item)
    return duplicates

# 示例用法
my_lst = [1, 2, 3, 4, 3, 2, 1, 5]
result = find_duplicates(my_lst)
print(result)  # 输出 [1, 2, 3]

In this example, the input list my_lst contains duplicate values of 1, 2, and 3. The code will identify these duplicates and store them in a list called result, then print them out in the end.