Writing a sorting algorithm from scratch in Python3.6

Question

I am trying to create an original sorting algorithm for my home work for school but i can't get it to work and I don't understand why.

def sa(x):
    print(x)
    i = 0
    s_array = []

    while x:
        for x[i] in x:
            if x[i] == min(x):
                s_array.append(x.pop(i))
                i = 0
            elif x[i] == max(x):
                s_array.append(x.pop(i))
                i = 0
            else:
                i += 1

    print(s_array)

I know I shouldn't have print functions in the program but i wanted it to be concise and packaged. so this is the output i get:

>>> sa([89, 23, 33, 45, 10, 12, 45, 45, 45])
[89, 23, 33, 45, 10, 12, 45, 45, 45]
[89, 45, 45, 45, 45, 45, 45, 45, 12]

I had the code like this:

def sa(x):
    print(x)
    i = 0
    s_array = []

    while x:
        for x[i] in x:
            if x[i] == min(x):
                s_array.append(x.pop(i))
                i = 0
            else:
                i += 1

print(s_array)

but was getting this as the output and thought i had to add the max() elif:

>>> sa([89, 23, 33, 45, 10, 12, 45, 45, 45])
[89, 23, 33, 45, 10, 12, 45, 45, 45]
[10, 45, 45, 45, 45, 45, 45, 45, 45]

please help.

Answer 1

the way your for loop is written you are assigning x[i] to an element in x according to iteration, consider this:

i = 0
x = ["a","b","c","d","e"]

for x[i] in x:
    print(x)

This will display the following:

['a', 'b', 'c', 'd', 'e']
['b', 'b', 'c', 'd', 'e']
['c', 'b', 'c', 'd', 'e']
['d', 'b', 'c', 'd', 'e']
['e', 'b', 'c', 'd', 'e']

Notice that the first element x[0] is changing to each element of the list as the list is iterated over, and when i changes it basically mixes up the elements of the list in a predictable but rarely useful way. instead since you only want to loop while there is still elements in the list just remove the inner for loop:

while x:
    if x[i] == min(x):
        s_array.append(x.pop(i))
        i = 0
    else:
        i += 1