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Python

Posted by Peter Smith
Peter Smith
1,550 Points

Not fully understanding @classmethod

I have rewatched the video and have tried looking to see if their was a question like this on treehouse but found their wasn't. Here is the code challenge: "Let's practice using @classmethod! Create a class method in Letter named from_string that takes a string like "dash-dot" and creates an instance with the correct pattern (['_', '.'])." I had some trouble understanding the point of classmethod and staticmethod and am getting frustrated with course.

morse.py 
class Letter:
    def __init__(self, pattern=None):
        self.pattern = pattern

    def __iter__(self):
        yield from self.pattern

    def __str__(self):
        output = []
        for blip in self:
            if blip == '.':
                output.append('dot')
            else:
                output.append('dash')
        return '-'.join(output)

    @classmethod
    def from_string(cls, dashdot):
        for dash in dashdot:
            print(dash)
        for dot in dashdot:
            print(dot)



class S(Letter):
    def __init__(self):
         pattern = ['.', '.', '.']
            super().__init__(pattern)

2 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,454 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,454 Points

You are on the right path. Here are the next steps:

  • dashdot is a string with “dash”s and “dot”s separated by hyphens (“-“). you will need to use the split('-') method to get each item that might be a dot or a dash.
  • with a single for loop, create a list of “.” and “_”
  • the cls parameter points to the current class. You can use cls(dot_dash_list) to create a new instance of Letter using the list created in the previous step
  • return this new instance

Post back if you need more help. Good luck!!!

Kautilya Kondragunta
Kautilya Kondragunta
492 Points
Kautilya Kondragunta
Kautilya Kondragunta
492 Points 
class Letter:
    def __init__(self, pattern=None):
        self.pattern = pattern

    def __iter__(self):
        yield from self.pattern

    def __str__(self):
        output = []
        for blip in self:
            if blip == '.':
                output.append('dot')
            else:
                output.append('dash')
        return '-'.join(output)

    @classmethod
    def from_string(cls, str_pattern):
        x = str_pattern.split('-')
        for item in x:
            if x[x.index(item)] == 'dash':
                x[x.index(item)] = '_'
            elif x[x.index(item)] == 'dot':
                x[x.index(item)] = '.'
        return cls(x)