How to define toString method?

Question

I have just almost finished my assignment and now the only thing I have left is to define the tostring method shown here.

import math

class RegularPolygon:
  def __init__(self, n = 1, l = 1):
    self.__n = n
    self.__l = l

  def set_n(self, n):
    self.__n = n

  def get_n(self):
    return self.__n

  def addSides(self, x):
    self.__n = self.__n + x

  def setLength(self, l ):
    self.__l = l

  def getLength(self):
    return self.__l 

  def setPerimeter(self):
    return (self.__n * self.__l )

  def getArea(self):
    return (self.__l ** 2 / 4 * math.tan(math.radians(180/self.__n)))

  def toString(self):
    return
x = 3
demo_object = RegularPolygon (3, 1)
print(demo_object.get_n() , demo_object.getLength())
demo_object.addSides(x)
print(demo_object.get_n(), demo_object.getLength())
print(demo_object.getArea())
print(demo_object.setPerimeter())

Basically the tostring on what it does is return a string that has the values of the internal variables included in it. I also need help on the getArea portion too. Assignment instructions

Please type in your requirements as text so they can be easily read. — Kirk Strauser, Dec 15 '20 at 17:27
Currently `toString` returns `None`. Have you attempted to implement anything there? What happened? — jonrsharpe, Dec 15 '20 at 17:29
You are writing what I like to call "Pava", code that is written like Java with just enough Python syntax to be executed. — Klaus D., Dec 15 '20 at 17:30
Yeah I just don't know what to return which in the assignment it says to return the internal variables included in it. So what would I put in it and then I'll do the rest of the assignment so I can turn it in since my teacher has been absent. — Javesike1262, Dec 15 '20 at 17:35
Using `toString()` would be very strange when you can use `__repr__` and `__str__` — JeffUK, Dec 15 '20 at 17:37
Do you need to return something like "RegularPolygon(3, 1)"? If so you should return `f'{self.__class__.__name__}({self.__n}, {self.__l})'` — Roy Cohen, Dec 15 '20 at 17:40
Where would I put that, I feel like those methods would be easier. — Javesike1262, Dec 15 '20 at 17:41

dwb · Answer 1 · 2020-12-15T19:07:19.510

The assignment says

... printing a string representation of a RegularPolygon object.

So I would expect you get to choose a suitable "representation". You could go for something like this:

return f'{self.__n+2} sided regular polygon of side length {self.__l}'

or as suggested by @Roy Cohen

return f'{self.__class__.__name__}({self.__n}, {self.__l})'

However, as @Klaus D. wrote in the comments, Python is not Java, and as such has its own standards and magic methods to use instead.

I would recommend reading this answer for an explanation between the differences between the two built-in string representation magic-methods: __repr__ and __str__. By implementing these methods, they will automatically be called whenever using print() or something similar, instead of you calling .toString() every time.

Now to address the getters and setters. Typically in Python you avoid these and prefer using properties instead. See this answer for more information, but to summarise you either directly use an objects properties, or use the @property decorator to turn a method into a property.

Edit

Your area formula is likely an error with order-of-operations. Make sure you are explicit with which operation you're performing first:

return self.__l ** 2 / (4 * math.tan(math.radians(180/self.__n)) )

This may be correct :)

Just to clarify, you don't need to use `property` in this case, just use the fields themselves. But you need to know that `property` exists in case you'd like to ever change the implementation of your class. — Roy Cohen, Dec 15 '20 at 17:48

How to define toString method?

1 Answers1