numbers
--- 數值的抽象基底類別¶
原始碼:Lib/numbers.py
The numbers
module (PEP 3141) defines a hierarchy of numeric
abstract base classes which progressively define
more operations. None of the types defined in this module are intended to be instantiated.
- class numbers.Number¶
數值階層結構的基礎。如果你只想確認引數 x 是不是數值、並不關心其型別,請使用
isinstance(x, Number)
。
數值的階層¶
- class numbers.Complex¶
這個型別的子類別描述了複數並包含適用於內建
complex
型別的操作。這些操作有:complex
和bool
的轉換、real
、imag
、+
、-
、*
、/
、**
、abs()
、conjugate()
、==
以及!=
。除-
和!=
之外所有操作都是抽象的。- real¶
為抽象的。取得該數值的實數部分。
- imag¶
為抽象的。取得該數值的虛數部分。
- abstractmethod conjugate()¶
為抽象的。回傳共軛複數,例如
(1+3j).conjugate() == (1-3j)
。
- class numbers.Real¶
To
Complex
,Real
adds the operations that work on real numbers.簡單的說,有
float
的轉換、math.trunc()
、round()
、math.floor()
、math.ceil()
、divmod()
、//
、%
、<
、<=
、>
、和>=
。實數同樣提供
complex()
、real
、imag
和conjugate()
的預設值。
- class numbers.Rational¶
Real
的子型別,並增加了numerator
和denominator
這兩種特性。它也會提供float()
的預設值。numerator
和denominator
的值必須是Integral
的實例且denominator
要是正數。- numerator¶
為抽象的。
- denominator¶
為抽象的。
給型別實作者的註記¶
實作者需注意,相等的數值除了大小相等外,還必須擁有同樣的雜湊值。當使用兩個不同的實數擴充時,這可能是很微妙的。例如,fractions.Fraction
底下的 hash()
實作如下:
def __hash__(self):
if self.denominator == 1:
# Get integers right.
return hash(self.numerator)
# Expensive check, but definitely correct.
if self == float(self):
return hash(float(self))
else:
# Use tuple's hash to avoid a high collision rate on
# simple fractions.
return hash((self.numerator, self.denominator))
加入更多數值 ABC¶
當然,還有更多用於數值的 ABC,如果不加入它們就不會有健全的階層。你可以在 Complex
和 Real
中加入 MyFoo
,像是:
class MyFoo(Complex): ...
MyFoo.register(Real)
實作算術操作¶
We want to implement the arithmetic operations so that mixed-mode
operations either call an implementation whose author knew about the
types of both arguments, or convert both to the nearest built in type
and do the operation there. For subtypes of Integral
, this
means that __add__()
and __radd__()
should be
defined as:
class MyIntegral(Integral):
def __add__(self, other):
if isinstance(other, MyIntegral):
return do_my_adding_stuff(self, other)
elif isinstance(other, OtherTypeIKnowAbout):
return do_my_other_adding_stuff(self, other)
else:
return NotImplemented
def __radd__(self, other):
if isinstance(other, MyIntegral):
return do_my_adding_stuff(other, self)
elif isinstance(other, OtherTypeIKnowAbout):
return do_my_other_adding_stuff(other, self)
elif isinstance(other, Integral):
return int(other) + int(self)
elif isinstance(other, Real):
return float(other) + float(self)
elif isinstance(other, Complex):
return complex(other) + complex(self)
else:
return NotImplemented
Complex
的子類別有 5 種不同的混合型別操作。我將上面提到所有不涉及 MyIntegral
和 OtherTypeIKnowAbout
的程式碼稱作「模板 (boilerplate)」。a
是 Complex
之子型別 A
的實例 (a : A <: Complex
),同時 b : B <: Complex
。我將要計算 a + b
:
If
A
defines an__add__()
which acceptsb
, all is well.If
A
falls back to the boilerplate code, and it were to return a value from__add__()
, we'd miss the possibility thatB
defines a more intelligent__radd__()
, so the boilerplate should returnNotImplemented
from__add__()
. (OrA
may not implement__add__()
at all.)Then
B
's__radd__()
gets a chance. If it acceptsa
, all is well.如果沒有成功回退到模板,就沒有更多的方法可以去嘗試,因此這裡將使用預設的實作。
如果
B <: A
,Python 會在A.__add__
之前嘗試B.__radd__
。這是可行的,因為它是透過對A
的理解而實作的,所以這可以在交給Complex
之前處理好這些實例。
If A <: Complex
and B <: Real
without sharing any other knowledge,
then the appropriate shared operation is the one involving the built
in complex
, and both __radd__()
s land there, so a+b
== b+a
.
由於大部分對任意給定類型的操作都十分相似的,定義一個為任意給定運算子生成向前 (forward) 與向後 (reverse) 實例的輔助函式可能會非常有用。例如,fractions.Fraction
使用了:
def _operator_fallbacks(monomorphic_operator, fallback_operator):
def forward(a, b):
if isinstance(b, (int, Fraction)):
return monomorphic_operator(a, b)
elif isinstance(b, float):
return fallback_operator(float(a), b)
elif isinstance(b, complex):
return fallback_operator(complex(a), b)
else:
return NotImplemented
forward.__name__ = '__' + fallback_operator.__name__ + '__'
forward.__doc__ = monomorphic_operator.__doc__
def reverse(b, a):
if isinstance(a, Rational):
# Includes ints.
return monomorphic_operator(a, b)
elif isinstance(a, Real):
return fallback_operator(float(a), float(b))
elif isinstance(a, Complex):
return fallback_operator(complex(a), complex(b))
else:
return NotImplemented
reverse.__name__ = '__r' + fallback_operator.__name__ + '__'
reverse.__doc__ = monomorphic_operator.__doc__
return forward, reverse
def _add(a, b):
"""a + b"""
return Fraction(a.numerator * b.denominator +
b.numerator * a.denominator,
a.denominator * b.denominator)
__add__, __radd__ = _operator_fallbacks(_add, operator.add)
# ...