Learn Interfaces by Building an Equation Solver - Step 38

Python
1

Tell us what’s happening:

Admitting defeat on this one. I can’t see what is wrong. I thought there was a problem with a and b not being defined with the solve method and accessed them with self. but that didn’t make a difference.

Your code so far

from abc import ABC, abstractmethod
import re


class Equation(ABC):
    degree: int
  
    def __init__(self, *args):
        if (self.degree + 1) != len(args):
            raise TypeError(
                f"'Equation' object takes {self.degree + 1} positional arguments but {len(args)} were given"
            )
        if any(not isinstance(arg, (int, float)) for arg in args):
            raise TypeError("Coefficients must be of type 'int' or 'float'")
        if args[0] == 0:
            raise ValueError("Highest degree coefficient must be different from zero")
        self.coefficients = {(len(args) - n - 1): arg for n, arg in enumerate(args)}

    def __init_subclass__(cls):
        if not hasattr(cls, "degree"):
            raise AttributeError(
                f"Cannot create '{cls.__name__}' class: missing required attribute 'degree'"
            )

    def __str__(self):
        terms = []
        for n, coefficient in self.coefficients.items():
            if not coefficient:
                coefficient
            if n == 0:
                terms.append(f'{coefficient:+}')
            elif n == 1:
                terms.append(f'{coefficient:+}x')
            else:
                terms.append(f"{coefficient:+}x**{n}")
        equation_string = ' '.join(terms) + ' = 0'
        return re.sub(r"(?<!\d)1(?=x)", "", equation_string.strip("+"))        

    @abstractmethod
    def solve(self):
        pass
        
    @abstractmethod
    def analyze(self):
        pass
        
class LinearEquation(Equation):
    degree = 1
    
    def solve(self):
        a, b = self.coefficients.values()
        x = -b / a
        return x

    def analyze(self):
        slope, intercept = self.coefficients.values()
        return {'slope': slope, 'intercept': intercept}

class QuadraticEquation(Equation):
    degree = 2

    def __init__(self, *args):
        super().__init__(*args)
        a, b, c = self.coefficients.values()
        self.delta = b**2 - 4 * a * c

# User Editable Region

    def solve(self):
        if self.delta < 0:
            return []
        root1 = (-self.b + (self.delta)**0.5) / (2 * self.a)
        root2 = (-self.b - (self.delta)**0.5) / (2 * self.a)
        return [root1, root2]

# User Editable Region

    def analyze(self):
        pass


lin_eq = LinearEquation(2, 3)
print(lin_eq)
quadr_eq = QuadraticEquation(11, -1, 1)
print(quadr_eq)

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/127.0.0.0 Safari/537.36 Edg/127.0.0.0

Challenge Information:

Learn Interfaces by Building an Equation Solver - Step 38

1 Like
2

Assign them the same way you do in the __init__ function.

Since it’s a different function you will need to assign them again, the a,b,c variables created in __init__ are local to the function and no accessible by self. as you’ve discovered.

If they had been initialized as self.a in __init__ they would be accessible.

3

I need the little hand slapping the head emoji! Many thanks, I am learning.

1 Like
4

I think it’s more common to see self variables in __init__ which would be more accessible but always good to check for the scope of the variables.