Reference · Math

math.prod

math.prod(list | null, num=) -> num

What it does

The product of a list of numbers, as Python's math.prod, times a start value that is 1 by default. The result is an int while the list and the start are all ints, and a float as soon as one of them is a float. An empty list gives the start value.

Examples

print(math.prod([2, 3, 4]), math.prod([2, 3.5]), math.prod([0.5, 4]))print(math.prod([2, 3], 10), type_of(math.prod([2, 3])))

24 7.0 2.060 int

Edge cases

• An empty list, or null, gives the start: 1 without one, else what was given, so math.prod([], 2.5) is 2.5, a float.
• A float start makes the result a float: math.prod([2, 3], 1.0) is 6.0.
• Ints multiply exactly, and a product past what an int holds (about 9.2 × 10¹⁸) is a runtime error, integer overflow, not a float; Python's int would keep growing. A float product that overflows is inf, silently.
• math.prod(range(1, n + 1)) is math.factorial(n).

print(math.prod([]), math.prod(null), math.prod([], 2.5), math.prod([2, 3], 1.0))print(math.prod([1e308, 10]), math.prod(range(1, 6)) == math.factorial(5))

1 1 2.5 6.0inf true

print(math.prod([9223372036854775807, 2]))

line 1: integer overflow

Errors

A list item that is not a number is a runtime error, not an error value; so is an argument that is not a list or null.

print(math.prod([2, "x"]))

line 1: `math.prod` expects numbers, got str

print(math.prod(3))

line 1: `math.prod` expects a list as argument 1, got int

Chaining

A list in a pipeline is the first argument, so xs | math.prod multiplies it out:

print([1, 2, 3, 4] | math.prod)print([1.1, 1.05, 0.9] | math.prod | round(3))

241.04

See also

sum, math.fsum, math.sumprod, vec.cumprod, math.factorial

Edit this page on GitHub · every example's output was made by running it (tools/refcheck.mjs) · questions on Discord or r/quillo