Flatten a Nested List Using List Comprehension in Python

In Python, you can flatten a nested list using list comprehension by iterating through each sublist and extracting its elements into a single-level list. This approach is both concise and efficient, making it an excellent choice for handling nested structures.

Examples

1. Flattening a Simple Nested List

Here, we have a nested list containing multiple sublists, and we use list comprehension to flatten it into a single list.

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# Nested list
nested_list = [[1, 2, 3], [4, 5], [6, 7, 8]]

# Flattening using list comprehension
flattened_list = [item for sublist in nested_list for item in sublist]

# Printing the flattened list
print("Flattened List:", flattened_list)

Explanation:

  • nested_list: A list containing sublists.
  • for sublist in nested_list: Iterates through each sublist.
  • for item in sublist: Extracts each element from the sublist.
  • [item for sublist in nested_list for item in sublist]: Generates a new flattened list.

Output:

Flattened List: [1, 2, 3, 4, 5, 6, 7, 8]

2. Flattening a List with Mixed Data Types

We can use the same method to flatten a nested list containing different data types.

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# Nested list with mixed data types
nested_list = [["apple", "banana"], [1, 2, 3], [True, False]]

# Flattening using list comprehension
flattened_list = [item for sublist in nested_list for item in sublist]

# Printing the flattened list
print("Flattened List:", flattened_list)

Explanation:

  • The nested list contains strings, integers, and boolean values.
  • List comprehension iterates through each sublist and extracts elements while maintaining data types.

Output:

Flattened List: ['apple', 'banana', 1, 2, 3, True, False]

3. Flattening a Deeply Nested List (One Level)

If we have a more deeply nested list where each sublist contains other sublists, this method will only flatten it one level.

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# Deeply nested list
nested_list = [[1, [2, 3]], [4, 5], [6, [7, 8]]]

# Flattening using list comprehension (one level)
flattened_list = [item for sublist in nested_list for item in (sublist if isinstance(sublist, list) else [sublist])]

# Printing the flattened list
print("Flattened List:", flattened_list)

Explanation:

  • The nested list contains elements where some sublists have another level of nesting.
  • The isinstance(sublist, list) check ensures we handle non-list elements correctly.
  • This approach flattens only one level, so deeper nested lists remain unflattened.

Output:

Flattened List: [1, [2, 3], 4, 5, 6, [7, 8]]

4. Flattening a List of Tuples

List comprehension can also flatten a nested list containing tuples.

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# Nested list with tuples
nested_list = [(1, 2), (3, 4), (5, 6)]

# Flattening using list comprehension
flattened_list = [item for sublist in nested_list for item in sublist]

# Printing the flattened list
print("Flattened List:", flattened_list)

Explanation:

  • Each tuple is treated as a sublist.
  • List comprehension iterates through each tuple and extracts elements.

Output:

Flattened List: [1, 2, 3, 4, 5, 6]

Conclusion

Depending on the structure of your nested list, you can:

  1. Use [item for sublist in nested_list for item in sublist] for simple nested lists.
  2. Handle different data types, including strings, numbers, and boolean values.
  3. Flatten a list of tuples similarly.
  4. Use additional conditions to partially flatten deeply nested lists.