Learn Interfaces by Building an Equation Solver - Step 35

Python
1

Tell us what’s happening:

First of i had to check online to see how to represent the digits before i found out that i was supposed to use \d. Then i tried to put just 1 after it, since i assumed that i was supposed to replace the 1 with the empty string but unfortunately i noticed it was removing the other 1’s. I finally found a way to replace -1 coefficient but it wouldn’t make use of the empty string and now i am guessing that it is because of that that i am unable to pass to the next step, so i need guidance to move.

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(r'(?<!\d)-1x', '-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

Modify your regex pattern

The instructions only ask you to modify the regex pattern, nothing else

return re.sub('1', '', equation_string.strip('+'))

The regex pattern is only the first argument of sub() which is '1', you shouldn’t change anything else.

Modify your regex pattern to use a negative lookbehind so that the character 1 is substituted only if not preceded by a digit.

This is all you need to do, you’ve made some other changes that aren’t in the instructions.

1 Like
3

This is what the instructions say to do:

Just try to follow each instruction, don’t try to guess ahead and do more.

1 Like
4

Wow thank you so much, you know i had done this before but because it wasn’t giving me a correct equation so to say, i didn’t even realise that i had already answered what i was requested to answer. Thank you so much, i am very grateful.

1 Like