Erle Robotics Learning Python GitBook Free

Exercises:Classes

Exercise 1

Follow the steps:

• Create a class, Triangle. Its __init__() method should take self, angle1, angle2, and angle3 as arguments. Make sure to set these appropriately in the body of the __init__()method.
• Create a variable named number_of_sides and set it equal to 3.
• Create a method named check_angles. The sum of a triangle's three angles is It should return True if the sum of self.angle1, self.angle2, and self.angle3 is equal 180, and False otherwise.
• Create a variable named my_triangle and set it equal to a new instance of your Triangle class. Pass it three angles that sum to 180 (e.g. 90, 30, 60).
• Print out my_triangle.number_of_sides and print out my_triangle.check_angles().

Exercise 2

Define a class called Songs, it will show the lyrics of a song. Its __init__() method should have two arguments:selfanf lyrics.lyricsis a list. Inside your class create a method called sing_me_a_songthat prints each element of lyricson his own line. Define a varible:

happy_bday = Song(["May god bless you, ",
                   "Have a sunshine on you,",
                   "Happy Birthday to you !"])

Call the sing_me_songmehod on this variable.

Exercise 3

Define a class called Lunch.Its __init__() method should have two arguments:selfanf menu.Where menu is a string. Add a method called menu_price.It will involve a ifstatement:

• if "menu 1" print "Your choice:", menu, "Price 12.00", if "menu 2" print "Your choice:", menu, "Price 13.40", else print "Error in menu".

To check if it works define: Paul=Lunch("menu 1") and call Paul.menu_price().

Exercise 4

Define a Point3D class that inherits from object Inside the Point3D class, define an __init__() function that accepts self, x, y, and z, and assigns these numbers to the member variables self.x,self.y,self.z. Define a __repr__() method that returns "(%d, %d, %d)" % (self.x, self.y, self.z). This tells Python to represent this object in the following format: (x, y, z). Outside the class definition, create a variable named my_point containing a new instance of Point3D with x=1, y=2, and z=3. Finally, print my_point.

Solutions

Exercise 1

>>> class Triangle(object):
...     def __init__(self,angle1,angle2,angle3):
...         self.angle1=angle1
...         self.angle2=angle2
...         self.angle3=angle3
...
...     number_of_sides=3
...     def check_angles(self):
...         if self.angle1+self.angle2+self.angle3 ==180:
...             return True
...         else:
...             return False
...
>>> class Equilateral(Triangle):
...   angle = 60
...   def __init__(self):
...        self.angle1 = self.angle2 = self.angle3 = self.angle
...
>>> my_triangle=Triangle(90,30,60)
>>>
>>> print my_triangle.number_of_sides
3
>>> print my_triangle.check_angles()
True
>>>

>>>

Exercise 2

>>> class Song(object):
...   def __init__(self, lyrics):
...      self.lyrics=lyrics
...   def sing_me_a_song(self):
...      for line in self.lyrics:
...           print line
...
>>>
>>> happy_bday = Song(["May god bless you, ",
...                    "Have a sunshine on you,",
...                    "Happy Birthday to you !"])
>>>
>>> print happy_bday.sing_me_a_song()
May god bless you,
Have a sunshine on you,
Happy Birthday to you !
None
>>>

Exercise 3

You can copy this code in a file called menu.py:

class Lunch(object):
    def __init__(self,menu):
      self.menu=menu

    def menu_price(self):
       if self.menu=="menu 1":
          print "Your choice:", menu, "Price 12.00"
       elif self.menu=="menu 2":
          print "Your choice:", menu, "Price 13.40"
       else:
          print "Error in menu"

Paul=Lunch("menu 1")
Paul.menu_price()

The execution should be:

root@erlerobot:~/Python_files# python menu.py
Your choice: menu 1 Price 12.00
root@erlerobot:~/Python_files#

Exercise 4

Copy the following code in a file called 3d.py:

class Point3D(object):
    def __init__(self,x,y,z):
        self.x=x
        self.y=y
        self.z=z

    def __repr__(self) :
       return "(%d, %d, %d)" % (self.x, self.y, self.z)



my_point=Point3D(1,2,3)
print my_point

Now, run the file:

root@erlerobot:~/Python_files# python menu.py
(1, 2, 3)
root@erlerobot:~/Python_files#