Learn Interfaces by Building an Equation Solver - Step 35

Python
1

Tell us what’s happening:

Hello,

I’ve modified the first argument in re.sub to use a negative lookbehind, but I’m unable to pass the step, even though the result appears “correct.” What am I missing here?

Thank you to anyone who can help me figure this out!

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:
                continue
            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'

# User Editable Region

        return re.sub('(?<!\d)1(?=x)', '', equation_string.strip('+'))        

# User Editable Region

    @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
   
    def solve(self):
        pass
    
    def analyze(self):
        pass


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

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Challenge Information:

Learn Interfaces by Building an Equation Solver - Step 35

2

You should have a negative lookbehind. But you have a negative lookbehind and a positive lookahead.

1 Like
3

Thank You @Dario_DC it worked.