Is there a way to properly continue this while loop? - python-3.x

Question

I have written a function where the input is a list of numbers (items), where the length is a multiple of 3.
I want to this function to continue, until there is only 1 value left in items.
while len(items) > 1:
for x in range(0, len(items), 3):
if items[x] < items[x+1] < items[x+2] or items[x] > items[x+1] >items[x+2] :
result.append(items[x+1])
elif items[x+1] < items[x] < items[x+2] or items[x+1] > items[x] > items[x+2]:
result.append(items[x])
else:
result.append(items[x+2])
items = result
break
return items

Answer 1

Taking a guess at what you needed and how your code should appear...
items = [99, 42, 17, 7, 1, 9, 12, 77, 15]
while len(items) > 1:
result = []
for x in range(0, len(items), 3):
a, b, c = items[x], items[x+1], items[x+2]
if a < b < c or a > b >c :
result.append(b)
elif b < a < c or b > a > c:
result.append(a)
else:
result.append(c)
items = result
print(items)
Introducing the variables a, b, and c helped me better read the code.

Answer 2

The logic is not quite right. Imagine a simple input of [1, 1, 0]. By looking at this, the median should be 1 but the use of > and < instead of <= and >= end up with the code entering the final else block because 1<1 is False and 1>1 is also False. The final else block sets the result equal to the third element, which is 0.
Switch your operators to >= and <= to fix this. The break at the bottom of your for loop immediately breaks after one iteration, so that also needs to be removed.
If you have a list of one element (3**0 = 1), you will end up with an IndexError when you try to get the 2nd and 3rd elements in your loop.
So we need to
Switch operators to test for equality as well
Remove the erroneous break
Handle the base case
def median_split3(items):
if len(items) == 1: # Base Case
return items[0]
while len(items) > 1:
result = []
for x in range(0, len(items), 3):
a, b, c = items[x:x+3]
if a <= b <= c or a >= b >= c:
result.append(b)
elif b <= a <= c or b >= a >= c:
result.append(a)
else:
result.append(c)
items = result
return items[0]
test1 = [99, 42, 17, 7, 1, 9, 12, 77, 15]
print(test1, "-->", median_split3(test1))
test2 = [1, 1, 0]
print(test2, "-->", median_split3(test2))
test3 = [0, 0, 1]
print(test3, "-->", median_split3(test3))
test4 = [9]
print(test4, "-->", median_split3(test4))
Output:
[99, 42, 17, 7, 1, 9, 12, 77, 15] --> 15
[1, 1, 0] --> 1
[0, 0, 1] --> 0
[9] --> 9