"""
A 2-dimensional vector class

    >>> v1 = Vector2d(3, 4)
    >>> x, y = v1
    >>> x, y
    (3.0, 4.0)
    >>> v1
    Vector2d(3.0, 4.0)
    >>> v1_clone = eval(repr(v1))
    >>> v1 == v1_clone
    True
    >>> print(v1)
    (3.0, 4.0)
    >>> octets = bytes(v1)
    >>> octets
    b'\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
    >>> abs(v1)
    5.0
    >>> bool(v1), bool(Vector2d(0, 0))
    (True, False)


Test of ``.frombytes()`` class method:

    >>> v1_clone = Vector2d.frombytes(bytes(v1))
    >>> v1_clone
    Vector2d(3.0, 4.0)
    >>> v1 == v1_clone
    True


Tests of ``format()`` with Cartesian coordinates:

    >>> format(v1)
    '(3.0, 4.0)'
    >>> format(v1, '.2f')
    '(3.00, 4.00)'
    >>> format(v1, '.3e')
    '(3.000e+00, 4.000e+00)'


Tests of the ``angle`` method::

    >>> Vector2d(0, 0).angle()
    0.0
    >>> Vector2d(1, 0).angle()
    0.0
    >>> epsilon = 10**-8
    >>> abs(Vector2d(0, 1).angle() - math.pi/2) < epsilon
    True
    >>> abs(Vector2d(1, 1).angle() - math.pi/4) < epsilon
    True


Tests of ``format()`` with polar coordinates:

    >>> format(Vector2d(1, 1), 'p')  # doctest:+ELLIPSIS
    '<1.414213..., 0.785398...>'
    >>> format(Vector2d(1, 1), '.3ep')
    '<1.414e+00, 7.854e-01>'
    >>> format(Vector2d(1, 1), '0.5fp')
    '<1.41421, 0.78540>'

"""

from array import array
import math


class Vector2d:
    typecode = 'd'

    def __init__(self, x, y):
        self.x = float(x)
        self.y = float(y)

    def __iter__(self):
        return (i for i in (self.x, self.y))

    def __repr__(self):
        class_name = type(self).__name__
        return '{}({!r}, {!r})'.format(class_name, *self)

    def __str__(self):
        return str(tuple(self))

    def __bytes__(self):
        return bytes(array(Vector2d.typecode, self))

    def __eq__(self, other):
        return tuple(self) == tuple(other)

    def __abs__(self):
        return math.hypot(self.x, self.y)

    def __bool__(self):
        return bool(abs(self))

    def angle(self):
        return math.atan2(self.y, self.x)

# tag::VECTOR2D_V2_FORMAT[]
    def __format__(self, fmt_spec=''):
        if fmt_spec.endswith('p'):  # <1>
            fmt_spec = fmt_spec[:-1]  # <2>
            coords = (abs(self), self.angle())  # <3>
            outer_fmt = '<{}, {}>'  # <4>
        else:
            coords = self  # <5>
            outer_fmt = '({}, {})'  # <6>
        components = (format(c, fmt_spec) for c in coords)  # <7>
        return outer_fmt.format(*components)  # <8>
# end::VECTOR2D_V2_FORMAT[]

    @classmethod
    def frombytes(cls, octets):
        memv = memoryview(octets).cast(cls.typecode)
        return cls(*memv)