# Learn Interfaces by Building an Equation Solver - Step 38

### 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.

``````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}

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)

``````

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### Challenge Information:

Learn Interfaces by Building an Equation Solver - Step 38

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.

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

1 Like

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.