Exercises

Книга: Practical Programming, Fourth Edition

Дальше: Chapter 15: Testing and Debugging

Here are some exercises for you to try on your own.

In this exercise, you will implement the class Country, which represents a country with a name, a population, and an area.

Here is a sample interaction from the Python shell:

	>>> canada = Country('Canada', 36991981, 9984670)
	>>> canada.name
	'Canada'
	>>> canada.population
	36991981
	>>> canada.area
	9984670

This code cannot be executed yet because the class Country does not exist. Define Country with an initializer (method __init__) that has four parameters: a country, its name, its population, and its area.

Consider this code:

	>>> canada = Country('Canada', 36991981, 9984670)
	>>> usa = Country('United States of America', 342034432, 9826675)
	>>> canada.is_larger(usa)
	True

In the class Country, define a method named is_larger that takes two Country objects and returns True if and only if the first has a larger area than the second.

Consider this code:
>>> canada.population_density()
3.704877677479576

In the class Country, define a method named population_density that returns the population density of the country (people per square kilometer).

Consider this code:

	>>> usa = Country('United States of America', 342034432, 9826675)
	>>> print(usa)
	United States of America has a population of 342034432 and is 9826675
	square km.

In class Country, define a method named __str__ that returns a string representation of the country in the format shown here.

After you have written __str__, this session shows that a __repr__ method would be useful:

	>>> canada = Country('Canada', 36991981, 9984670)
	>>> canada
	<exercise_country.Country object at 0x7f2aba30b550>
	>>> print(canada)
	Canada has population 36991981 and is 9984670 square km.
	>>> [canada]
	[<exercise_country.Country object at 0x7f2aba30b550>]
	>>> print([canada])
	[<exercise_country.Country object at 0x7f2aba30b550>]

Define the __repr__ method in Country to produce a string that behaves like this:

	>>> canada = Country('Canada', 36991981, 9984670)
	>>> canada
	Country('Canada', 36991981, 9984670)
	>>> [canada]
	[Country('Canada', 36991981, 9984670)]

In this exercise, you will implement a Continent class, which represents a continent with a name and a list of countries. Class Continent will use class Country from the previous exercise. If Country is defined in another module, you’ll need to import it.

Here is a sample interaction from the Python shell:

	>>> canada = country.Country('Canada', 36991981, 9984670)
	>>> usa = country.Country('United States of America', 342034432,
	... 9826675)
	>>> mexico = country.Country('Mexico', 132452034, 1943950)
	>>> countries = [canada, usa, mexico]
	>>> north_america = Continent('North America', countries)
	>>> north_america.name
	'North America'
	>>> for country in north_america.countries:
	print(country)

	Canada has a population of 36991981 and is 9984670 square km.
	United States of America has a population of 342034432 and is 9826675
	square km.
	Mexico has a population of 132452034 and is 1943950 square km.
	>>>

The code cannot be executed yet, because class Continent does not exist. Define Continent with an initializer (method __init__) that has three parameters: a continent, its name, and its list of Country objects.

Consider this code:
>>> north_america.total_population()
511478447

In class Continent, define a method named total_population that returns the sum of the populations of the countries on this continent.

Consider this code:

	>>> print(north_america)
	North America
	Canada has a population of 36991981 and is 9984670 square km.
	United States of America has a population of 342034432 and is 9826675
	square km.
	Mexico has a population of 132452034 and is 1943950 square km.

In class Continent, define a method named __str__ that returns a string representation of the continent in the format shown here.

In this exercise, you’ll write __str__ and __repr__ methods for several classes.
1. In class Student, write a __str__ method that includes all the Member information and in addition includes the student number, the list of courses taken, and the list of current courses.
2. Write __repr__ methods in classes Member, Student, and Faculty.
Create a few Student and Faculty objects and call str and repr on them to verify that your code does what you want it to.
Write a class called Nematode to keep track of information about C. elegans, including a variable for the body length (in millimeters; they are about 1 mm in length), gender (either hermaphrodite or male), and age (in days).

Include methods __init__, __repr__, and __str__.

Consider this code:

	>>> segment = LineSegment(Point(1, 1), Point(3, 2))
	>>> segment.slope()
	0.5
	>>> segment.length()
	2.23606797749979

In this exercise, you will write two classes, Point and LineSegment, so that you can run this code and get the same results.

Write a Point class with an __init__ method that takes two numbers as parameters.
In the same file, write a LineSegment class whose initializer takes two Points as parameters. The first Point should be the start of the segment.
Write a slope method in the class LineSegment that computes the slope of the segment. (Hint: The slope of a line is rise over run.)
Write a length method in class LineSegment that computes the length of the segment. (Hint: Use x ** n to raise x to the nth power. To compute the square root, raise a number to the (1/2) power or use math.sqrt.)

Назад: Classifying What You’ve Learned

Дальше: Chapter 15: Testing and Debugging

	>>> canada.population_density()
	3.704877677479576

	>>> north_america.total_population()
	511478447