Task: Quaternion type
C#: using System;

struct Quaternion : IEquatable<Quaternion>
{
    public readonly double A, B, C, D;

    public Quaternion(double a, double b, double c, double d)
    {
        this.A = a;
        this.B = b;
        this.C = c;
        this.D = d;
    }

    public double Norm()
    {
        return Math.Sqrt(A * A + B * B + C * C + D * D);
    }

    public static Quaternion operator -(Quaternion q)
    {
        return new Quaternion(-q.A, -q.B, -q.C, -q.D);
    }

    public Quaternion Conjugate()
    {
        return new Quaternion(A, -B, -C, -D);
    }

    
    public static implicit operator Quaternion(double d)
    {
        return new Quaternion(d, 0, 0, 0);
    }

    public static Quaternion operator +(Quaternion q1, Quaternion q2)
    {
        return new Quaternion(q1.A + q2.A, q1.B + q2.B, q1.C + q2.C, q1.D + q2.D);
    }

    public static Quaternion operator *(Quaternion q1, Quaternion q2)
    {
        return new Quaternion(
            q1.A * q2.A - q1.B * q2.B - q1.C * q2.C - q1.D * q2.D,
            q1.A * q2.B + q1.B * q2.A + q1.C * q2.D - q1.D * q2.C,
            q1.A * q2.C - q1.B * q2.D + q1.C * q2.A + q1.D * q2.B,
            q1.A * q2.D + q1.B * q2.C - q1.C * q2.B + q1.D * q2.A);
    }

    public static bool operator ==(Quaternion q1, Quaternion q2)
    {
        return q1.A == q2.A && q1.B == q2.B && q1.C == q2.C && q1.D == q2.D;
    }

    public static bool operator !=(Quaternion q1, Quaternion q2)
    {
        return !(q1 == q2);
    }

    #region Object Members

    public override bool Equals(object obj)
    {
        if (obj is Quaternion)
            return Equals((Quaternion)obj);

        return false;
    }

    public override int GetHashCode()
    {
        return A.GetHashCode() ^ B.GetHashCode() ^ C.GetHashCode() ^ D.GetHashCode();
    }

    public override string ToString()
    {
        return string.Format("Q({0}, {1}, {2}, {3})", A, B, C, D);
    }

    #endregion

    #region IEquatable<Quaternion> Members

    public bool Equals(Quaternion other)
    {
        return other == this;
    }

    #endregion
}

Python: from collections import namedtuple
import math

class Q(namedtuple('Quaternion', 'real, i, j, k')):
    'Quaternion type: Q(real=0.0, i=0.0, j=0.0, k=0.0)' 

    __slots__ = () 

    def __new__(_cls, real=0.0, i=0.0, j=0.0, k=0.0):
        'Defaults all parts of quaternion to zero'
        return super().__new__(_cls, float(real), float(i), float(j), float(k))

    def conjugate(self):
        return Q(self.real, -self.i, -self.j, -self.k)

    def _norm2(self):
        return sum( x*x for x in self)

    def norm(self):
        return math.sqrt(self._norm2())

    def reciprocal(self):
        n2 = self._norm2()
        return Q(*(x / n2 for x in self.conjugate())) 

    def __str__(self):
        'Shorter form of Quaternion as string'
        return 'Q(%g, %g, %g, %g)' % self

    def __neg__(self):
        return Q(-self.real, -self.i, -self.j, -self.k)

    def __add__(self, other):
        if type(other) == Q:
            return Q( *(s+o for s,o in zip(self, other)) )
        try:
            f = float(other)
        except:
            return NotImplemented
        return Q(self.real + f, self.i, self.j, self.k)

    def __radd__(self, other):
        return Q.__add__(self, other)

    def __mul__(self, other):
        if type(other) == Q:
            a1,b1,c1,d1 = self
            a2,b2,c2,d2 = other
            return Q(
                 a1*a2 - b1*b2 - c1*c2 - d1*d2,
                 a1*b2 + b1*a2 + c1*d2 - d1*c2,
                 a1*c2 - b1*d2 + c1*a2 + d1*b2,
                 a1*d2 + b1*c2 - c1*b2 + d1*a2 )
        try:
            f = float(other)
        except:
            return NotImplemented
        return Q(self.real * f, self.i * f, self.j * f, self.k * f)

    def __rmul__(self, other):
        return Q.__mul__(self, other)

    def __truediv__(self, other):
        if type(other) == Q:
            return self.__mul__(other.reciprocal())
        try:
            f = float(other)
        except:
            return NotImplemented
        return Q(self.real / f, self.i / f, self.j / f, self.k / f)

    def __rtruediv__(self, other):
        return other * self.reciprocal()

    __div__, __rdiv__ = __truediv__, __rtruediv__

Quaternion = Q       

q  = Q(1, 2, 3, 4)
q1 = Q(2, 3, 4, 5)
q2 = Q(3, 4, 5, 6)
r  = 7