PYTHON
Flattening a List of Nested Lists
Learn various Pythonic methods, including list comprehensions and `itertools.chain`, to flatten a list containing multiple sub-lists into a single, cohesive list for data processing.
import itertools
list_of_lists = [[1, 2, 3], [4, 5], [], [6]]
# Method 1: Using a simple list comprehension (for one level of nesting)
flattened_comprehension = [item for sublist in list_of_lists for item in sublist]
print(f"Flattened (list comprehension): {flattened_comprehension}")
# Method 2: Using itertools.chain.from_iterable (generally more memory efficient for large lists)
flattened_itertools = list(itertools.chain.from_iterable(list_of_lists))
print(f"Flattened (itertools.chain): {flattened_itertools}")
# Method 3: Flattening an arbitrarily nested list (using recursion for any depth)
def flatten_arbitrary_depth(nested_list):
for item in nested_list:
if isinstance(item, list) and not isinstance(item, (str, bytes)): # Exclude strings/bytes from being 'flattened'
yield from flatten_arbitrary_depth(item)
else:
yield item
deeply_nested_list = [1, [2, 3], [4, [5, 6, [7]]], 8, []]
flattened_deeply = list(flatten_arbitrary_depth(deeply_nested_list))
print(f"Flattened (arbitrary depth): {flattened_deeply}")
How it works: Flattening a list of lists into a single list is a common data preparation task. For a single level of nesting, a simple list comprehension is often the most readable and Pythonic. For larger lists or when memory efficiency is critical, `itertools.chain.from_iterable` is a performant alternative. If your list contains sub-lists nested at arbitrary depths, a recursive generator function is necessary to traverse all levels and yield individual elements.