3.2. Unary Special Methods

Unary operations involve only one object they are called on.

For example:

• str(obj)

• len(obj)

only accept a single object.

This means that the corresponding special method only has self as a parameter.

3.2.1. String - __str__

When str is called on an object the Python interpreter will call the object’s __str__ method, which must return a str value.

The returned string can be anything we choose, such as an attribute value or a formatted string combining multiple attributes together or something entirely different.

Examples

def __str__(self):
    return self.name

def __str__(self):
    return "{} is at your service!".format(self.name)

3.2.2. Length - __len__

When len() is called on an object, Python calls the object’s __len__ method, which must return an integer.

This is typically used when the object represents a collection or something measurable.

Examples

def __len__(self):
    return len(self.cargo)

def __len__(self):
    return self.fuel_weight  # Interpreted as fuel level

Code Challenge: Identify Yourself! Redux

The intergalactic parliament has now made it mandatory for Spaceships to identify themselves.

Complete the Spaceship class with __str__ and __repr__ methods that prints the name of the ship and the amount of fuel on board.

Requirements

Both __str__ and __repr__ methods must return a string of the form:

{name} [Fuel: {fuel_weight}/{fuel_capacity} ({fuel_percent}%)]

See example below.

The fuel_percent must be reported to 0 decimal places.

Note

Hint: You can call str(self) from __repr__ to save time.

Example

>>> xwing = Spaceship("X Wing", 500)
>>> xwing.refuel(100)
>>> print(xwing)
X Wing [Fuel: 100/500 (20%)]
>>> print(repr(xwing))
'X Wing [Fuel: 100/500 (20%)]'

Here is some code for you to start with:

class Spaceship:
    def __init__(self, name, fuel_capacity):
        self.name = name
        self.fuel_weight = 0
        self.fuel_capacity = fuel_capacity

    def refuel(self, weight):
        if self.fuel_weight + weight > self.fuel_capacity:
            self.fuel_weight = self.fuel_capacity
        else:
            self.fuel_weight += weight

    def fire_laser(self):
        if self.fuel_weight >= 10:
            self.fuel_weight -= 10

    # YOUR METHODS HERE


xwing = Spaceship("X Wing", 500)
xwing.refuel(500)  # Fill 'er up!

print(xwing)

Solution

Solution is locked