Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Python

leonardo valdes
leonardo valdes
12,384 Points
Posted by leonardo valdes
leonardo valdes
12,384 Points

@classmethod output question

I passed this code challenge but I was still confused on how classmethods work. I tried to use the from_string method using the string passed, but when I print it it prints the original string and not the dots and dashes that I was expecting. Am I using the class method incorrectly? What should I be doing?

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, string):
        entry = string.split('-')
        pattern = []
        for blip in entry:
            if blip == 'dot':
                pattern.append('.')

            else:
                pattern.append('_')
        return cls(pattern)


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

test = Letter.from_string('dash-dot-dash-dot')
print(test)
leonardo valdes
leonardo valdes
12,384 Points
leonardo valdes
leonardo valdes
12,384 Points

I figured out that using test.pattern outputs what I was looking for. So, that brings up another question: why does it print the original string when I put print(test), but not when i put print(test.pattern)? What is the difference?

1 Answer

andren
andren
28,558 Points
andren
andren
28,558 Points

When you pass something that is not a string into the print function it will automatically converting it to a string by calling the str method on the object. So when you call print(test) you are actually printing out whatever the test object's __str__ method produces.

The __str__ method on the Letter class loops through the pattern and returns the decoded version of it. That is why you get that version printed out.