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class Vec:
    """ A simple vector class

Instances of the Vec class  can be constructed from numbers

>>> a = Vec(1, 2, 3)
    >>> b = Vec(3, 2, 1)

added
    >>> a + b
    Vec(4, 4, 4)

subtracted
    >>> a - b
    Vec(-2, 0, 2)

and multiplied by a scalar on the left
    >>> 3.0 * a
    Vec(3.0, 6.0, 9.0)

or on the right
    >>> a * 3.0
    Vec(3.0, 6.0, 9.0)
    """
    def __init__(self, *v):
        self.v = list(v)

@classmethod
    def fromlist(cls, v):
        if not isinstance(v, list):
            raise TypeError
        inst = cls()
        inst.v = v
        return inst

def __repr__(self):
        args = ', '.join(repr(x) for x in self.v)
        return 'Vec({0})'.format(args)

def __len__(self):
        return len(self.v)

def __getitem__(self, i):
        return self.v[i]

def __add__(self, other):
        # Element-wise addition
        v = [x + y for x, y in zip(self.v, other.v)]
        return Vec.fromlist(v)

def __sub__(self, other):
        # Element-wise subtraction
        v = [x - y for x, y in zip(self.v, other.v)]
        return Vec.fromlist(v)

def __mul__(self, scalar):
        # Multiply by scalar
        v = [x * scalar for x in self.v]
        return Vec.fromlist(v)

__rmul__ = __mul__

def test():
    import doctest
    doctest.testmod()

test()

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