FAQ: Learn Python - Introduction to Classes - Class It Up

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This community-built FAQ covers the “Class It Up” exercise in Codecademy’s lessons on Python.

FAQs for the Codecademy Python exercise Class It Up:

• How do I add a member variable to the Triangle class?
  

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[rubypro38623]

Why does the method check_angles only take the argument self (i.e. def check_angles(self): ) as opposed to the three angles (i.e. def check_angles(self, angle1, angle2, angle3):). Is it because the angles must be provided to exist in the triangle class?

Additionally, why is it not possible to use:

if angle1 + angle2 + angle 3 == 180

as opposed to:

if (self.angle1 + self.angle2 + self.angle3) == 180:

since we previously defined self.angle = angle in the init() ?

[mtf]

@rubypro38623

Why does the method check_angles only take the argument self

Because self is the context of the angles for that instance. We don’t need to pass them in, only access the instance variables.

@rubypro38623

why is it not possible to use:

if angle1 + angle2 + angle 3 == 180

Those variables do not exist in the context of the instance. When we first create the instance the variables are available, but if we return to the method at some time later, they will not. Only their self.attributes still exist.

[jim.jamz]

For this exercise, I have created the Triangle class and the check_angles class method. I have also created the number_of_sides member variable, which according to this, is in the correct place. Here is my code:

class Triangle(object):
  number_of_sides = 3

  def __init__(self, angle1, angle2, angle3):
    self.angle1 = angle1
    self.angle2 = angle2
    self.angle3 = angle3
    
    def check_angles(self):
      if (self.angle1 + self.angle2 + self.angle3 == 180):
        return True
      else:
        return False

When I select ‘Run’, no error appears, but the ‘Next’ button is not enabled. After multiple attempts at ‘Run’, I am asked whether I want to view the solution.

Because no error is displayed in either the console or in tooltip form, how can I improve my code, if it is indeed wrong?

[mtf]

The check_angles method looks to be indented enough to be in the code block of the __init__() method.

[jim.jamz]

Yes, I believe you’re correct. But shouldn’t that produce an indentationError in the console? This is very difficult to spot and especially if you don’t go full-screen in the editor.

[mtf]

@jim.jamz

But shouldn’t that produce an indentationError

Not if the interpreter simply sees it as code in the other method. While it is still indented, create an instance and then try to run the method.

[jim.jamz]

OK, thanks. Ultimately, I would have expected the error to get passed to something further down the exception stack so that at least something is displayed in the console. Perhaps because there is no actual error in the end, and the program simply runs then stops, it is one of those few exceptional circumstances where the codecademy tooltip may have to intervene to guide the user. In this situation, even viewing the solution and comparing it visually, it may not be immediately clear to the user.

[mtf]

That will be for the CC curriculum team. We have no hand in the lessons, only the questions that are asked in the forums.

Tell me, what happened when you ran the method on your instance?

Belay. I’ve run the check…

Traceback (most recent call last):
  File "C:/Users/Mr/AppData/Local/Programs/Python/Python38/Scripts/triangle_class.py", line 16, in <module>
    print (equilateral.check_angles())
AttributeError: 'Triangle' object has no attribute 'check_angles'

The interpreter could not find the method.

[jim.jamz]

Perhaps the error should then appear in the console as it does in your IDE?

[mtf]

It would if you tried to run the method on a Triangle instance.

Leave the code indented as before and try this line…

print (Triangle(30, 60, 90).check_angles())

Traceback (most recent call last):
  File "<pyshell#54>", line 1, in <module>
    Triangle(30, 60, 90).check_angles()
AttributeError: 'Triangle' object has no attribute 'check_angles'

[array9123272298]

Good day everyone,
Could someone have a look at the screenshot of the code? I do not understand the error that pops up. In the console I have an output True, if you change the values, it gives False, but neverthless it sees it as an error.

Thanks in advance for clarification!

[array9123272298]

I even checked the solution to figure out the Error and it does not look differently from mine. Strange.

[victoria-dr]

Double-check your conditional statement in check_angles(). Remember that the angles of a triangle should add up to 180 degrees.