reduce()

The reduce() function returns an aggregated value that results from the application of a function to an iterable. The function is applied to the first pair of items in the iterable and the resulting value is then used with the next item in the sequence, this process repeats through item n.

reduce(func_name, iterable, initializer)

The func_name is the function to be applied to the iterable and can be a lambda function or the name of any defined function. The iterable contains the items, such as a list, the function will act on. The initializer is an optional parameter that provides the ability to substitute an initial value for the first calculation. With the initializer set, the first calculation will be between the initializer value and the first item in the sequence in lieu of the first and second items of the sequence.

The following example uses reduce() to sum all the values in the nums list and add this value to an initial sum start:

from functools import reduce
start = 30
nums = [x for x in range(10)]

print(reduce(lambda x, y: x + y, nums, start))
# Output: 75

reduce() can be used to return the minimum value within a list:

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