Build a function that takes a list of strings as input, returns a boolean indicating whether all the-CodePudding

I am write a function that can return Boolean if every string in a list contains the word 'red'. Below is the code that I came up with, it worked well for test case AllRed(["red hat", "a pair of red shoes", "three red apples"]); and test case AllRed(["red hat", "white shirt", "black eyes"]). However, when I tested it with an empty list, it returned True.

def AllRed  (lst):
 return all("red" in i for i in lst)
AllRed([])

It is supposed to return false for empty list.

CodePudding user response：

The all() function is required to return True for empty lists. This ensures that the following equivalence will always be true:

all(list1) and all(list2) == all(list1   list2)

When list1 is empty, list1 list2 is the same as list2. So we need all(list1) to return True.

Similarly, any() returns False for an empty list, so that

any(list1) or any(list2) == any(list1   list2)

is true.

CodePudding user response：

It is because when your iterable (lst) is empty, there is nothing to iterate over; and if you see how all() works, it returns True when iterable is empty.

See how all() works