"""
Demonstration of idiomatic use of reduce() in Python.
Although Python encourages using built‑ins like sum(), max(), or comprehensions,
reduce() is still useful when you want to collapse a sequence into a single value
using a custom rule.
We will:
1. Define a function that uses reduce() to compute the product of numbers.
2. Define a function that uses reduce() to flatten a list of lists.
3. Show how reduce() works step‑by‑step.
"""
from functools import reduce
def multiply_all(numbers):
"""
Multiply all numbers in a list using reduce().
The lambda receives the accumulated value and the next element.
Equivalent to: (((n1 * n2) * n3) * n4) ...
"""
return reduce(lambda acc, x: acc * x, numbers, 1)
# The third argument (1) is the initializer, ensuring correct behavior even for empty lists.
def flatten_list(list_of_lists):
"""
Flatten a list of lists using reduce().
Each step concatenates the accumulated list with the next sublist.
"""
return reduce(lambda acc, lst: acc + lst, list_of_lists, [])
# Using [] as initializer ensures the accumulator starts as an empty list.
def demo_reduce_steps(numbers):
"""
Show how reduce() processes elements step-by-step.
This is purely illustrative.
"""
def step(acc, x):
print(f"acc={acc}, next={x} -> new_acc={acc * x}")
return acc * x
return reduce(step, numbers, 1)
# ------------------------------
# Usage
# ------------------------------
nums = [2, 3, 4]
nested = [[1, 2], [3], [4, 5]]
product_result = multiply_all(nums)
flattened_result = flatten_list(nested)
print("Product of numbers:", product_result)
print("Flattened list:", flattened_result)
print("\nStep-by-step reduce demonstration:")
demo_reduce_steps(nums)
'''
run:
Product of numbers: 24
Flattened list: [1, 2, 3, 4, 5]
Step-by-step reduce demonstration:
acc=1, next=2 -> new_acc=2
acc=2, next=3 -> new_acc=6
acc=6, next=4 -> new_acc=24
'''
