Question

Hey guys so this is my first year programming and I started with python. I am understanding the programming fairly well but I need help with this homework question.

I have to use a list as my parameter and then return the number of different values in the list. The example list in the question is [1, 4, 1, 7, 6, 1, 4, 3] and therefore the returned value should be 5.

Now I know my method of solving it is probably not concise or elegant but if someone could help me and tell me what to change so it works I would greatly appreciate it.

def count(mylist):
    newlist = []
    newlist.append(mylist[0])
    stor = False
    for i in mylist:
        stor = False
        for j in newlist:
            if j == i:
                stor == True
        if not stor:
            newlist.append(i)
    return newlist

Answer 1

At first, a fixed version of your program

def count(mylist):
    newlist = []
    newlist.append(mylist[0])
    stor = False
    for i in mylist:
        stor = False
        for j in newlist:
            if j == i:
                stor = True # stor == True test for equality
        if not stor:
            newlist.append(i)
    return len(newlist) # you do not want the list itself but its length

And here some suggestions:

• you do not need to initialize stor outside the outer loop. This is done two lines later again.
• consider a break in the inner loop – this speeds things up a bit (no unneeded comparison)
• newlist can be initialized to an empty list without appending the first item. The algorithm stays valid (the inner loop have zero iterations the first time)

here as code-example:

def count(mylist):
    newlist = []
    for i in mylist:
        stor = False
        for j in newlist:
            if j == i:
                stor = True
                break
        if not stor:
            newlist.append(i)
    return len(newlist)

And more elegant (and pythonic): use the in-syntax 😉

def count(mylist):
    newlist = []
    for i in mylist:
        if i not in newlist:
            newlist.append(i)
    return len(newlist)

Basically item in something_iterable returns true, if item can be found in something_iterable. Most collection of items is iterable (e.g. lists, sets, strings … 'a' in 'abc' returns true )

and the most pythonic way but without for/while-loops:

def count(mylist):
    return len(set(mylist))

Please look into other answers for an explanation.