# python 类切片的实现

A multi-dimensional `Vector` class, take 3

A `Vector` is built from an iterable of numbers::

```>>> Vector([3.1, 4.2])
Vector([3.1, 4.2])
>>> Vector((3, 4, 5))
Vector([3.0, 4.0, 5.0])
>>> Vector(range(10))
Vector([0.0, 1.0, 2.0, 3.0, 4.0, ...])```

Tests with 2-dimensions (same results as `vector2d_v1.py`)::

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

Test of `.frombytes()` class method:

```>>> v1_clone = Vector.frombytes(bytes(v1))
>>> v1_clone
Vector([3.0, 4.0])
>>> v1 == v1_clone
True```

Tests with 3-dimensions::

```>>> v1 = Vector([3, 4, 5])
>>> x, y, z = v1
>>> x, y, z
(3.0, 4.0, 5.0)
>>> v1
Vector([3.0, 4.0, 5.0])
>>> v1_clone = eval(repr(v1))
>>> v1 == v1_clone
True
>>> print(v1)
(3.0, 4.0, 5.0)
>>> abs(v1)  # doctest:+ELLIPSIS
7.071067811...
>>> bool(v1), bool(Vector([0, 0, 0]))
(True, False)```

Tests with many dimensions::

```>>> v7 = Vector(range(7))
>>> v7
Vector([0.0, 1.0, 2.0, 3.0, 4.0, ...])
>>> abs(v7)  # doctest:+ELLIPSIS
9.53939201...```

Test of `.__bytes__` and `.frombytes()` methods::

```>>> v1 = Vector([3, 4, 5])
>>> v1_clone = Vector.frombytes(bytes(v1))
>>> v1_clone
Vector([3.0, 4.0, 5.0])
>>> v1 == v1_clone
True```

Tests of sequence behavior::

```>>> v1 = Vector([3, 4, 5])
>>> len(v1)
3
>>> v1[0], v1[len(v1)-1], v1[-1]
(3.0, 5.0, 5.0)```

Test of slicing::

```>>> v7 = Vector(range(7))
>>> v7[-1]
6.0
>>> v7[1:4]
Vector([1.0, 2.0, 3.0])
>>> v7[-1:]
Vector([6.0])
>>> v7[1,2]
Traceback (most recent call last):
...
TypeError: Vector indices must be integers```

Tests of dynamic attribute access::

```>>> v7 = Vector(range(10))
>>> v7.x
0.0
>>> v7.y, v7.z, v7.t
(1.0, 2.0, 3.0)```

Dynamic attribute lookup failures::

```>>> v7.k
Traceback (most recent call last):
...
AttributeError: 'Vector' object has no attribute 'k'
>>> v3 = Vector(range(3))
>>> v3.t
Traceback (most recent call last):
...
AttributeError: 'Vector' object has no attribute 't'
>>> v3.spam
Traceback (most recent call last):
...
AttributeError: 'Vector' object has no attribute 'spam'```

Tests of preventing attributes from 'a' to 'z'::

```>>> v1.x = 7
Traceback (most recent call last):
...
>>> v1.w = 7
Traceback (most recent call last):
...
AttributeError: can't set attributes 'a' to 'z' in 'Vector'```

Other attributes can be set::

```>>> v1.X = 'albatross'
>>> v1.X
'albatross'
>>> v1.ni = 'Ni!'
>>> v1.ni
'Ni!'```

"""

from array import array import reprlib import math import numbers

class Vector: typecode = 'd'

```def __init__(self, components):
self._components = array(self.typecode, components)

def __iter__(self):
return iter(self._components)

def __repr__(self):
components = reprlib.repr(self._components)
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 __eq__(self, other):
return tuple(self) == tuple(other)

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

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

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

def __getitem__(self, index):
cls = type(self)
if isinstance(index, slice):
return cls(self._components[index])
elif isinstance(index, numbers.Integral):
return self._components[index]
else:
msg = '{.__name__} indices must be integers'
raise TypeError(msg.format(cls))```

# BEGIN VECTOR_V3_GETATTR

```shortcut_names = 'xyzt'

def __getattr__(self, name):
cls = type(self)  # <1>
if len(name) == 1:  # <2>
pos = cls.shortcut_names.find(name)  # <3>
if 0 <= pos < len(self._components):  # <4>
return self._components[pos]
msg = '{.__name__!r} object has no attribute {!r}'  # <5>
raise AttributeError(msg.format(cls, name))```

# BEGIN VECTOR_V3_SETATTR

```def __setattr__(self, name, value):
cls = type(self)
if len(name) == 1:  # <1>
if name in cls.shortcut_names:  # <2>
elif name.islower():  # <3>
error = "can't set attributes 'a' to 'z' in {cls_name!r}"
else:
error = ''  # <4>
if error:  # <5>
msg = error.format(cls_name=cls.__name__, attr_name=name)
raise AttributeError(msg)
super().__setattr__(name, value)  # <6>```

# END VECTOR_V3_SETATTR

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

0 条评论

• ### IOS UIResponder 触碰拖动图像

override func touchesMoved(_ touches：Set<UITouch>, with event：UIEvent？) { //需要先...

• ### python 通过字符串方式调用方法operator.methodcaller

class Point: def init(self, x, y): self.x = x self.y = y

• ### go语言中json转成map结构

package main import ( "encoding/json" "fmt" ) //把请求包定义成一个结构体 type Reques...

• ### Go语言中json转成map结构

package main import ( "encoding/json" "fmt" ) //把请求包定义成一个结构体 type Reques...

• ### go语言中json转成map结构

package main import ( "encoding/json" "fmt" ) //把请求包定义成一个结构体 type Reques...

• ### go语言中json转成map结构

package main import ( "encoding/json" "fmt" ) //把请求包定义成一个结构体 type Reques...

• ### 基础：为什么计算机只认识0和1？

端午节放假休息，我正在家里面吹着空调，吃着西瓜，看着《这就是街舞》，女朋友在一旁看某游戏主播的直播。我隐约中听到她手机中传来主播的一句话：“朋友们，听懂我的意思...

• ### 为什么计算机只认识0和1？

计算机（computer）俗称电脑，是现代一种用于高速计算的电子计算机器，可以进行数值计算，又可以进行逻辑计算，还具有存储记忆功能。是能够按照程序运行，自动、高...

• ### 宝利通Polycom CX600版本升级

最近项目需要，把宝利通Polycom CX600版本从4.0.7577.4455升级到最新版本4.0.7577.4512。