How to Remove Duplicates From a Python List

Removing duplicates from a list in Python can be achieved using various approaches. Here are five examples along with step-by-step explanations and their outputs:

Example 1: Using a loop and a new list

def remove_duplicates(input_list):
    output_list = []
    for item in input_list:
        if item not in output_list:
            output_list.append(item)
    return output_list

# Example usage
input_list = [1, 2, 2, 3, 4, 4, 5]
result = remove_duplicates(input_list)
print(result)

Explanation:

Define a function remove_duplicates that takes an input list.
Initialize an empty list output_list.
Iterate through each item in the input list.
If the item is not already in the output list, append it.
Return the output list.

Output:

[1, 2, 3, 4, 5]

Example 2: Using set() function

def remove_duplicates(input_list):
    return list(set(input_list))

# Example usage
input_list = [1, 2, 2, 3, 4, 4, 5]
result = remove_duplicates(input_list)
print(result)

Explanation:

Define a function remove_duplicates that takes an input list.
Convert the input list to a set, which automatically removes duplicates.
Convert the set back to a list and return it.

Output:

[1, 2, 3, 4, 5]

Example 3: Using list comprehension

def remove_duplicates(input_list):
    return [item for index, item in enumerate(input_list) if item not in input_list[:index]]

# Example usage
input_list = [1, 2, 2, 3, 4, 4, 5]
result = remove_duplicates(input_list)
print(result)

Explanation:

Define a function remove_duplicates that takes an input list.
Use list comprehension to iterate through each item and filter out duplicates by checking if the item appears before the current index.

Output:

[1, 2, 3, 4, 5]

Example 4: Using OrderedDict

from collections import OrderedDict

def remove_duplicates(input_list):
    return list(OrderedDict.fromkeys(input_list))

# Example usage
input_list = [1, 2, 2, 3, 4, 4, 5]
result = remove_duplicates(input_list)
print(result)

Explanation:

Import OrderedDict from the collections module.
Define a function remove_duplicates that takes an input list.
Create an ordered dictionary from the input list, which automatically removes duplicates.
Convert the ordered dictionary back to a list and return it.

Output:

[1, 2, 3, 4, 5]

Example 5: Using a loop and the count() method

def remove_duplicates(input_list):
    output_list = []
    for item in input_list:
        if input_list.count(item) > 1:
            input_list.remove(item)
    return input_list

# Example usage
input_list = [1, 2, 2, 3, 4, 4, 5]
result = remove_duplicates(input_list)
print(result)

Explanation:

Define a function remove_duplicates that takes an input list.
Iterate through each item in the input list.
If the count of the item is greater than 1 (meaning it is a duplicate), remove it from the input list.
Return the modified input list.

Output: