Chapter 13: Classes and Objects
===============================
The answers on this page show ONE way to solve the :ref:`exercises <classes-and-objects-exercises>`.
However, there are usually OTHER ways to accomplish the same thing. This is OK!
A suggested solution is ONE way to solve the problem, not the ONLY way.
Chapter Sandbox
---------------
Use the editor below to test out any of the solutions!
.. raw:: html
<iframe src="https://trinket.io/embed/python3/560cc5a91d" width="100%" height="400" frameborder="1" marginwidth="0" marginheight="0" allowfullscreen></iframe>
Solutions
---------
In these exercises, you will create a ``Robot`` class and use it to create
four ``Robot`` objects. You will also practice writing functions that display
information about the objects and race them against each other.
.. _chp13part1:
Part 1: Create a New Class
^^^^^^^^^^^^^^^^^^^^^^^^^^
Open up the starter code and notice that it imports the ``random`` module.
Below the ``import`` statement, define the ``Robot`` class.
Add Properties to ``Robot``
^^^^^^^^^^^^^^^^^^^^^^^^^^^
1. Inside the class, define the ``__init__`` method. It should include
parameters for ``self``, ``name``, ``mass``, and ``year``.
.. sourcecode:: Python
:linenos:
class Robot:
#set up Robot Object Properties
def __init__(self, name, mass, year):
self.name = name
self.mass = mass
self.year = year
2. Give a default value to ``year``.
.. sourcecode:: Python
:linenos:
def __init__(self, name, mass, year = 1942):
Before you move on, test your new class! In ``main()``:
.. sourcecode:: Python
:linenos:
#a. Call the ``Robot`` class to create a new object. Assign it to a variable.
robot_bob = Robot("Bob", 42, 1974)
#Code to test creation of Robot class
#b. Use dot notation to ``print`` the values for each property.
print("\nRobot Information:")
print(" Name: " + robot_bob.name)
print(" Mass: " + str(robot_bob.mass) + "kg")
print(" Year Made: " + str(robot_bob.year))
print(" Distance Traveled: " + str(robot_bob.distance))
Add Methods to ``Robot``
^^^^^^^^^^^^^^^^^^^^^^^^
1. Below ``__init__``, define a second method called ``move()``. This method should:
.. sourcecode:: Python
:linenos:
#a. Only take the ``self`` parameter.
def move(self):
#c. Increase the ``distance`` property by the number of steps.
steps_taken = random.randint(1,10)
self.distance += steps_taken
2. Add the ``__str__`` method to return a string of the object properties.
.. sourcecode:: Python
:linenos:
#returns a string of robot properties of our choosing
def __str__(self):
output = "\nRobot Info: \n Name: {0}\n Mass: {1} kg\n Year made: {2}\n Distance traveled: {3}"
return output.format(self.name, self.mass, self.year, self.distance)
Test your methods! In ``main()``:
.. sourcecode:: Python
:linenos:
#a. ``print`` the ``Robot`` object to check the output.
#Code that calls the __str__ method
print(robot_bob)
:ref:`Back to the exercises <chp13partNewClass>`.
.. _chp13part2:
Part 2: Create Objects
^^^^^^^^^^^^^^^^^^^^^^
In part 1, you defined a class and created one ``Robot`` object in ``main()``.
Now create three more objects:
3. Use a mass value from ``25`` to ``40``. (*Bonus*: Use ``randint`` to
generate the mass value instead of hard-coding a number when you call the
class).
.. sourcecode:: Python
:linenos:
robot_unimate = Robot("Unimate",random.randint(25, 40), 1954)
robot_terry = Robot("Terry", random.randint(25, 40), random.randint(1923, 2022))
robot_jones = Robot("Jones", 42 , 1969)
You now have 4 total robots. Add another statement in ``main()`` where you
place the objects inside a list. Assign the collection to a variable called
``robots``.
.. sourcecode:: Python
:linenos:
robots = [robot_bob, robot_unimate, robot_terry, robot_jones]
Update Distances
^^^^^^^^^^^^^^^^
Use a loop to iterate through the ``robots`` list. For each object, assign a
random value to the ``distance`` property, from ``1000`` to ``3000`` steps.
.. sourcecode:: Python
:linenos:
#add in main
for robot in robots:
robot.distance = random.randint(1000, 3000)
:ref:`Back to the exercises <chp13partCreateObjects>`.
.. _chp13part3:
Part 3: Find Oldest Robot
^^^^^^^^^^^^^^^^^^^^^^^^^
Between the class and ``main()``, define a function called ``oldest_robot``. It
should:
2. Use a loop to iterate through the list.
.. sourcecode:: Python
:linenos:
def oldest_robot(robot_list):
robot_year = []
for robot in robot_list:
robot_born = robot.year
robot_year.append(robot_born)
#index value of oldest robot in robot_list
oldest = robot_year.index(min(robot_year))
4. If two robots have the same ``year`` value, then the one with the largest
``distance`` will be older.
.. sourcecode:: Python
:linenos:
#year oldest robot was made
oldest_robot_year = robot_year[oldest]
#checking to see if more then one robot born in oldest_robot_year
same_year = robot_year.count(oldest_robot_year)
#more then one robot born in oldest year
if same_year > 1:
#distance in steps of oldest robot
oldest_robot_distance = robot_list[oldest].distance
for index in range(len(robot_year)):
year = robot_list[index].year
if year == oldest_robot_year:
if robot_list[index].distance > oldest_robot_distance:
oldest_robot_distance = robot_list[index].distance
oldest = index
#Return the index value for the oldest robot in the list.
return oldest
In ``main()``, call the ``oldest_robot`` function and use ``robots`` for the
argument. Assign the returned index to a new variable.
.. sourcecode:: Python
:linenos:
#create variable and call function
index_oldest = oldest_robot(robots)
Print out a message describing the result:
.. sourcecode:: Python
:linenos:
print(f"\n{robots[index_oldest].name} is the oldest robot (made in {robots[index_oldest].year},
{robots[index_oldest].distance} steps).\n")
:ref:`Back to the exercises <chp13partFindOldest>`.
.. _chp13part4:
Part 4: Robot Races
-------------------
Now it's time for the robots to compete against each other! Define the
``robot_race`` function that takes a list of robots as a parameter.
Within the function:
1. Each robot takes a turn running a race.
2. A robot runs the race by calling its ``move()`` method several times.
3. A robot is done with the race when it moves 30 steps or more.
4. Create a new list to store how many turns it takes each robot to complete
the race. Use the string: ``'____ took ____ turns to take 30 steps.'``
Fill in the blanks with the robot’s name and race result.
.. sourcecode:: Python
:linenos:
#create empty list for results of each robot(part 4)
results = []
#loop thru robots(part 1)
for robot in robots:
#set variables
steps = 0
turns = 0
#keep taking turns until robot gets at least 30 steps(part 2-3)
while steps <= 30:
steps += robot.move()
turns += 1
#add string with robot results to results list(part 4)
results.append(f"{robot.name} took {turns} turns to take {steps} steps.")
5. Print the results to the console (one robot per line).
.. sourcecode:: Python
:linenos:
#in main
#create variable and call function
robot_race_results = robot_race(robots)
for result in robot_race_results:
print(result)
:ref:`Back to the exercises <chp13partRobotRaces>`.