missing var

import sympy

def solve_equation(e, **kwargs):
    e = e.replace('^', '**')
    left, right = e.split('=')
    left_expr = sympy.sympify(left)
    right_expr = sympy.sympify(right)
    equation = sympy.Eq(left_expr, right_expr)

    symbols = equation.free_symbols
    symbol_names = {str(s): s for s in symbols}

    knowns = {}
    missing_var = None
    for name, value in kwargs.items():
        if name in symbol_names:
            if value is None:
                if missing_var is not None:
                    raise ValueError("Only one variable can be missing")
                missing_var = symbol_names[name]
            else:
                knowns[symbol_names[name]] = value
        else:
            raise ValueError(f"Variable '{name}' not found in equation")

    if missing_var is None:
        raise ValueError("No missing variable specified (use None)")

    equation_sub = equation.subs(knowns)
    solution = sympy.solve(equation_sub, missing_var)

    if not solution:
        raise ValueError("No solution found")

    result = solution[0]
    if result.is_real and result.is_number:
        return float(result) if not result.is_Integer else int(result)
    return result

# Example usage:
# print(solve_equation('a+b*c=d', a=1, b=2, d=5, c=None))  # Output: 2.0
# print(solve_equation('a=exp(x)', a=2, x=None))           # Output: 0.6931471805599453