Practicing python. Nothing to see here. Move on!

python_practice.py

def per_octal(perm_string):
    permStr = ""
    res = 0
    for i in range(len(perm_string)):
        perm = perm_string[i]
        if perm == 'r':
            res += 4
        elif perm == 'w':
            res += 2
        elif perm == 'x':
            res += 1
        elif perm == '-':
            res += 0
        if (i+1 % 3 == 0):
            permStr = str(res)
            res = 0
    return int(permStr)

def tuple_slice(startIndex, endIndex, tup):
    res = ""
    resList = []
    for ele in tup[startIndex:endIndex]:
        resList.append(str(ele))
    return (',').join(resList)

def change_date_format(dates):
    resList = []
    dateStr = ""

    for date in dates:
        dateStr = ""
        form1 = []
        form2 = []
        form1 = date.split('/')
        form2 = date.split('-')
        if len(form1) == 3:
            if len(form1[0]) == 4:
                for ele in form1:
                    dateStr += ele
                resList.append(dateStr)
            else:
                dateStr = form1[2] + form1[1] + form1[0]
                resList.append(dateStr)
        elif len(form2) == 3:
            dateStr = form2[2] + form2[0] + form2[1]
            resList.append(dateStr)
    return resList