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Python语言程序设计(美-梁勇)第7章习题解答(英文)

Chapter 7 Objects and Classes

1. See the section "Defining Classes for Objects."

2. Define the initializer, create data fields, and define methods.

3. Use a constructor

4. The name of the initializer is __init__.

5. The self refers to the object itself. Through self, the

members of the object can be accessed.

6. The syntax for constructing an object is

ClassName(arguments)

The arguments of the constructor match the parameters

in the __init__ method without self.

The constructor first creates an object in the memory

and then invokes the initializer.

7. Initializer is a special method that is called when

creating an object.

8.The object member access operator is the dot (.).

9.You need to pass an argument in the constructor A() to

invoke the class A’s initializer.

10.(a) The constructor should be defined as __init__(self).

(b) radius = 3 should be self.radius = 3

11.

count is 100

times is 0

12.

count is 0

n is 1

13.__i is a private data field and cannot be accessed from

outside of the class.

14. Correct. The printout is Welcome.

15.__on is a private data field and cannot be accessed

outside the class.

The way to fix it is to add a getter method for the

Boolean property as follows:

class A:

def __init__(self, on):

self.__on = not on

def isOn(self):

return self.__on

def main():

a = A(False)

print(a.isOn())

main() # Call the main function

16.T wo benefits: (1) for protecting data and (2) for easy

to maintain the class.

In Python, private data fields are defined with two

leading underscores.

17.A dd two underscores as the prefix for the method name.

18.S ee the text