map in Python with multiple arguments, including one with a default value

Question

I am using Python3.6 and am trying to figure out ways in which we can use map with multiple arguments.

When I run,

def multiply(x, y, z):
    return x * y * z

products = map(multiply, [3,6], [1,8], [3,5])

list(products) returns [9, 240] as expected

However, when I specify a default value for z,

def multiply(x, y, z = [3,5]):
    return x * y * z

products = map(multiply, [3,6], [1,8])

list(product) returns

[[3, 5, 3, 5, 3, 5],
 [3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5,
  3,
  5]]

Why does Python differ in the way it runs map in the two scenarios?

Answer 1

When you set the default value of z during execution with map this happens:

3 * 1 * [3,5]
6 * 8 * [3,5]

Therefore your output, for map to work as you intend you should explicitly give the list as one of it arguments and in your case the default value of z is not a direct argument of map. Hope this makes sense.