Exercises
Here are some exercises for you to try on your own. Solutions are available at http://pragprog.com/titles/gwpy3/practical-programming.
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In this exercise, you will implement class Country, which represents a country with a name, a population, and an area.
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Here is a sample interaction from the Python shell:
>>> canada = Country('Canada', 34482779, 9984670) >>> canada.name 'Canada' >>> canada.population 34482779 >>> canada.area 9984670 This code cannot be executed yet because class Country does not exist. Define Country with a constructor (method __init__) that has four parameters: a country, its name, its population, and its area.
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Consider this code:
>>> canada = Country('Canada', 34482779, 9984670) >>> usa = Country('United States of America', 313914040, 9826675) >>> canada.is_larger(usa) True In 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.
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Consider this code:
>>> canada.population_density() 3.4535722262227995 In class Country, define a method named population_density that returns the population density of the country (people per square kilometer).
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Consider this code:
>>> usa = Country('United States of America', 313914040, 9826675) >>> print(usa) United States of America has a population of 313914040 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.
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After you have written __str__, this session shows that a __repr__ method would be useful:
>>> canada = Country('Canada', 34482779, 9984670) >>> canada <exercise_country.Country object at 0x7f2aba30b550> >>> print(canada) Canada has population 34482779 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', 34482779, 9984670) >>> canada Country('Canada', 34482779, 9984670) >>> [canada] [Country('Canada', 34482779, 9984670)]
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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.
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Here is a sample interaction from the Python shell:
>>> canada = country.Country('Canada', 34482779, 9984670) >>> usa = country.Country('United States of America', 313914040, ... 9826675) >>> mexico = country.Country('Mexico', 112336538, 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 34482779 and is 9984670 square km. United States of America has a population of 313914040 and is 9826675 square km. Mexico has a population of 112336538 and is 1943950 square km. >>> The code cannot be executed yet, because class Continent does not exist. Define Continent with a constructor (method __init__) that has three parameters: a continent, its name, and its list of Country objects.
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Consider this code:
>>> north_america.total_population() 460733357 In class Continent, define a method named total_population that returns the sum of the populations of the countries on this continent.
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Consider this code:
>>> print(north_america) North America Canada has a population of 34482779 and is 9984670 square km. United States of America has a population of 313914040 and is 9826675 square km. Mexico has a population of 112336538 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.
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In this exercise, you’ll write __str__ and __repr__ methods for several classes.
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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.
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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.
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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__.
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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.
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Write a Point class with an __init__ method that takes two numbers as parameters.
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In the same file, write a LineSegment class whose constructor takes two Points as parameters. The first Point should be the start of the segment.
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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.)
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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.)
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