How does all() in python work on empty lists

Question

I am referring to the following python code

all(a==2 for a in my_list)

I expect the above code to return True if all the elements in my_list are 2. but when I make my_list empty and run it as

my_list = []
all(a==2 for a in my_list) 

it returns True as well. I am confused with this behaviour. Is it not supposed to return False as there is no element in my_list with value 2?

Answer 1

It's true because for every element in the list, all 0 of them, they all are equal to 2.

You can think of all being implemented as:

def all(list, condition):
  for a in list:
    if not condition(a):
      return false
  return true

Whereas any is:

def any(list, condition):
  for a in list:
    if condition(a):
      return true
  return false

That is to say, all is innocent until proven guilty, and any is guilty until proven innocent.