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Table of Contents
1. Use set() (easiest, but not keeping order)
2. Use dict.fromkeys() (recommended, keep order)
3. Use list to derive seen sets (custom logic, suitable for complex scenarios)
4. Remove duplicates of non-hashable types such as dictionaries in the list
Summary: Recommended usage
Home Backend Development Python Tutorial python remove duplicates from list example

python remove duplicates from list example

Jul 26, 2025 am 07:53 AM
java programming

To remove duplicate elements in Python list, 1. Use set(): It is suitable for situations where elements are immutable and do not care about order. The syntax is list(set(original_list)), but it will disrupt the original order; 2. Use dict.fromkeys(): Recommended method, applicable to Python 3.7, which can maintain the order of the first occurrence of elements. The syntax is list(dict.fromkeys(original_list)), and the code is concise and efficient; 3. Use list derivation and seed collection: It is suitable for scenarios where deduplication logic is required. By traversing the list and recording the seen elements with the set, ensuring uniqueness; 4. When dealing with non-hashable types such as dictionaries, you can deduplicate based on specific keys (such as 'id'), manually traversing and using the seed collection to make sure that the key value is not added repeatedly. Summary: In general, it is recommended to use dict.fromkeys() to maintain order. If you do not need order, you can use set(). For complex structures, manually traversal and add seed sets to complete deduplication.

python remove duplicates from list example

There are several ways to remove duplicate elements from Python lists, and the following are several common and practical examples.

python remove duplicates from list example

1. Use set() (easiest, but not keeping order)

If the elements in the list are all immutable types (such as integers, strings, tuples), and you don't care about the order of the elements , you can directly convert them to collections and then return to the list:

 original_list = [1, 2, 2, 3, 4, 4, 5]
unique_list = list(set(original_list))
print(unique_list) # The output may be [1, 2, 3, 4, 5] (the order may vary)

?? Note: set will disrupt the original order because the set is unordered.

python remove duplicates from list example

This is the simplest way to keep the first occurrence of elements , and it works in Python 3.7 (because the dictionary guarantees the insertion order starting from 3.7):

 original_list = [1, 2, 2, 3, 4, 4, 5]
unique_list = list(dict.fromkeys(original_list))
print(unique_list) # Output: [1, 2, 3, 4, 5]

? Advantages: The code is concise, keeps order and is fast.

python remove duplicates from list example

3. Use list to derive seen sets (custom logic, suitable for complex scenarios)

If you want to have more flexibility in controlling deduplication logic (such as handling dictionary lists), you can use a secondary collection to record the seen elements:

 original_list = [1, 2, 2, 3, 4, 4, 5]
see = set()
unique_list = []

for item in original_list:
    if item not in see:
        seen.add(item)
        unique_list.append(item)

print(unique_list) # Output: [1, 2, 3, 4, 5]

This method is suitable for scenarios where custom "judgment repetition" logic is required.


4. Remove duplicates of non-hashable types such as dictionaries in the list

If the list is a dictionary or a list that is not hashable, you cannot use set or dict.fromkeys() directly. You can deduplicate based on a certain key:

 data = [
    {'id': 1, 'name': 'Alice'},
    {'id': 2, 'name': 'Bob'},
    {'id': 1, 'name': 'Alice'}, # Repeat]

see = set()
unique_data = []

for item in data:
    key = item['id'] # If key not in seed:
        seen.add(key)
        unique_data.append(item)

print(unique_data)
# Output: [{'id': 1, 'name': 'Alice'}, {'id': 2, 'name': 'Bob'}]

  • Generally (elements can be hashed, and order must be maintained)? Use list(dict.fromkeys(lst))
  • Don't care about order, pursue speed? Use list(set(lst))
  • Complex structures (such as dictionaries)? Manually traverse the seen collection

Basically all this is not complicated but it is easy to ignore the order issue.

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