I am not getting it please help me

# We are creating a class called 'Letter
class Letter:
    # we then create an __init__ which is the first thing that runs when you call the class Letter
    # the __init__ has the following arguments; self, and pattern=None
    # self refers to the class Letter
    # pattern is variable set to None
    def __init__(self, pattern=None):
        # We have to define the variable pattern this the following code:
        self.pattern = pattern

    # __str__ is a method that is used to represent string of the object
    # we give the arguments, self and pattern to it
    # again, self just refers to the class Letter
    # and pattern refers to the pattern that is assign in __init__ method
    def __str__(self, pattern):
        # creating a variable called 's' with an empty string
        # this will hold our morse code
        s =""
        # we then look through all the pattern
        # for example, pattern = ['.', '.', '.'], pattern is an array
        # that holds multiple elements. with for item in pattern we
        # are going to look through each element and do the following:
        for item in pattern:
            # if (item) 'element' is a '.'(period), we add it as 'dot' in s (variable)
            if item == '.':
                s += 'dot'
            # if (item) 'element' is a '_'(underscore), we add it as 'dash' in s (variable)
            elif item == '_':
                s += 'dash'
            # else, just add what ever item is to s (variable)
            else:
                s += item
        # then we are just returning the variable s
        return s

# Here we create a child class S of Letter
# meaning that Letter is parent of S
# the reason why we create a child class is
# because of inheritance 
class S(Letter):
    # again __init___ is the method that will run first when you call child S Class
    # __init__ is not referring to Letter's __init__, they are their own methods, for now
    def __init__(self):
        # here we create the 'Morse code' pattern
        pattern = ['.', '.', '.']
        #super() allows us to call the parent Letter and give it the pattern array
        #that would later be converted into the desired pattern, ex.: 'dashdashdash'/'dotdashdot'
        super().__init__(pattern)