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Python

Posted by Mohammad Aslam
Mohammad Aslam
6,053 Points

Morse code and __str__

Hi there,

I don't quite understand what this challenge is asking for. Can someone please have a look at my code and advise me if I am on the right track and what to do next?

I also don't understand the str method. What is this particular method supposed to do? Why is it a special method? Can someone please explain?

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

    def __str__(self):
        list1 = []
        for item in pattern:
            if item == ".":
                list1.append("dot")
            if item == "_":
                list1.append("dash")
        return "-".join(list1)


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

2 Answers

Wade Williams
Wade Williams
24,476 Points
Wade Williams
Wade Williams
24,476 Points

You're definitely on the right track! You just need to add self to pattern in your for loop.

for item in self.pattern:

When you add a __str__ function to your class, you're telling python what it should do when str() is call on an instance of that class. If your class doesn't have a __str__ method, you'll get something like <__main__.S object at 0x0287F890> which is the instance's location in memory. This is undesirable, so we tell python to create a morse code string when str() is called on our class.

morse_code = S()

# without __str__ method in class
# <__main__.S object at 0x0287F890>
str(morse_code)

# with __str__ method in class
# "dot-dot-dot"
str(morse_code)

Dan Bader has a nice article on "dunder" methods:

https://dbader.org/blog/python-dunder-methods

Mohammad Aslam
Mohammad Aslam
6,053 Points
Mohammad Aslam
Mohammad Aslam
6,053 Points

Thanks a lot!

So if you try running str() on an instance of the class, instead of performing a string function on the instance, it somehow produces the memory location. And by using str, you can change this output to something else you set arbitrarily.

It makes more sense, but I don't understand completely. Why would you want to call str() on an instance anyway? How does it help you?