Data Attributes vs Parameter Names: What self Guarantees

Why does `self.x = x` guarantee every Coordinate carries an x, when the plain parameter `x` vanishes the moment `__init__` returns?

Finger exercises

Short drills on what this video just taught. Write the code, run the checks, and reveal the answer only if you are stuck.

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Exercise 1 of 5

Wearing both hats

Song is a brand new data type, but its body is empty so far. Put the implementer's hat on first: give Song an __init__ taking a title and a length in seconds, and store both of them as data attributes named title and seconds, so that every Song ever built is guaranteed to carry them.

Then swap hats and use the finished type: build the song "Blackbird", 138 seconds long, and assign that object itself to song.

class Song(object):
    """ A song with a title and a length in seconds """

    # your code here: write the __init__ method


# Build "Blackbird", 138 seconds long.
song = ...  # your code here

class Song(object):
    """ A song with a title and a length in seconds """

    # your code here: write the __init__ method


# Build "Blackbird", 138 seconds long.
song = ...  # your code here

Python runs in your browser

⌘/Ctrl + Enter runs

`song` is an object of type `Song`

every `Song` carries a title and a length

the song built is the one the prompt asked for

a second `Song` gets its own values

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