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from array import array
import reprlib
import math
import numbers
import functools
import operator
import itertools  # <1>


class Vector:
    typecode = 'd'

    def __init__(self, components):   # self._components 是“受保护的”实例属性
        self._components = array(self.typecode, components) # 分量保存在一个数组中

    def __iter__(self):
        return iter(self._components) # 支持迭代协议

    def __repr__(self):
        components = reprlib.repr(self._components) # reprlib.repr()获取有限长度表示
        components = components[components.find('['): -1]
        return 'Vector({})'.format(components)

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

    def __bytes__(self):
        return (bytes([ord(self.typecode)]) +
                bytes(self._components))

    def __abs__(self):
        return math.sqrt(sum(x * x for x in self))

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

    @classmethod
    def frombytes(cls, octets):
        typecode = chr(octets[0])
        memv = memoryview(octets[1: ]).cast(typecode)
        return cls(memv)