python 中 __truediv__ 的运算符重载
operator overloading for __truediv__ in python
我正在尝试重载 python 中的除法运算符。
class Fraction:
def __init__(self,top,bottom):
def gcd(m, n):
while m % n != 0:
old_m = m
old_n = n
m = old_n
n = old_m % old_n
return n
common = gcd(top,bottom)
self.num = top/common
self.den = bottom/common
def __str__ (self):
return str(self.num) + "/" + str(self.den)
def get_num(self):
return self.num
def get_den(self):
return self.den
def __add__(self, other_fraction):
new_num = self.num * other_fraction.den + self.den * other_fraction.num
new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
def __sub__(self, other_fraction):
new_num = self.num * other_fraction.den - self.den * other_fraction.num
new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
def __mul__ (self, other_fraction):
new_num = self.num * other_fraction.num
new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
def __truediv__(self, other_fraction):
new_num = self.num * other_fraction.den
new_den = self.den * other_fraction.num
return Fraction(new_num, new_den)
def __eq__(self, other):
first_num = self.num * other.den
second_num = other.num * self.den
return first_num == second_num
a = Fraction(10,20)
b = Fraction(30,20)
print a
print "numerator is",a.get_num()
print "denominator is",a.get_den()
print "equality is",(a==b)
print "sum is",(a+b)
print "difference is",(a-b)
print "product is",(a*b)
print "division is",(a/b)
但我在 __truediv__ 处收到错误消息：
TypeError: unsupported operand type(s) for /: 'instance' and
'instance'
代码有什么问题？
object.__truediv__() 特殊方法 仅 与 / 运算符一起使用，然后仅当您将 Python 编译器切换为使用真正的除法：
from __future__ import division
如果您没有使用该导入，/ 运算符会调用 object.__div__() special method（如果存在）。
另一方面，// 运算符调用您未实现的 object.__floordiv__() special method。
来自docs:
object.__div__(self, other)
object.__truediv__(self, other)
The division operator (/) is implemented by these methods. The
__truediv__() method is used when __future__.division is in effect, otherwise __div__() is used. If only one of these two methods is
defined, the object will not support division in the alternate
context; TypeError will be raised instead.
和here：
A future statement is a directive to the compiler that a particular
[python program] should be compiled using syntax or semantics that will be
available in a ... future release of Python. The future
statement is intended to ease migration to future versions of Python
that introduce incompatible changes to the language. It allows use of
the new features before the release in which the
feature becomes standard.
future_statement: from __future__ import feature
The features recognized by Python 2.x are unicode_literals,
print_function, absolute_import, division, generators, nested_scopes
and with_statement
现在，一些测试：
~$ python2.7
Python 2.7.6 (v2.7.6:3a1db0d2747e, Nov 10 2013, 00:42:54)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 3/2
1
>>> exit()
~$ python3.2
Python 3.2.3 (v3.2.3:3d0686d90f55, Apr 10 2012, 11:25:50)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 3/2
1.5
所以，你看，/ 运算符的效果在 python 3.x 中发生了变化。您也可以在下面的示例中看到这一点：
class Dog(object):
def __div__(self, other):
print("__div__ called")
def __truediv__(self, other):
print("__truediv__ called")
Dog() / Dog()
--output:--
~/python_programs$ python2.7 myprog.py
__div__ called
~/python_programs$ python3.4 myprog.py
__truediv__ called
因为 __truediv__ 不被 python 2.x 中的 / 运算符调用，覆盖 python [=54= 中的 __truediv__ ] 无效。
PEP 238 - PEP 238 -- Changing the Division Operator
We propose the following transitional measures:
- Classic division will remain the default in the Python 2.x
series; true division will be standard in Python 3.0.
- The // operator will be available to request floor[, i.e. integer,]
division unambiguously.
- The future division statement, spelled "from __future__ import
division", will change the / operator to mean true division
throughout the [program]
现在，看看这里发生了什么：
from __future__ import division
class Dog(object):
def __div__(self, other):
print("__div__ called")
def __truediv__(self, other):
print("__truediv__ called")
Dog() / Dog()
--output:--
~/python_programs$ python2.7 myprog.py
__truediv__ called
~/python_programs$ python3.4 myprog.py
__truediv__ called
现在，您在 python 2.x 中获得 python3.x 运算符的 / 效果。因此，现在您可以覆盖 __truediv__ 以使 / 运算符执行您想要的操作。
注意，如果你想在python3.x中进行整数除法，即3/2 => 1，那么你必须使用//运算符，它由[=实现28=]。同样，如果你在 python 2.x 中执行 from __future__ import division，那么要得到整数除法，你必须使用 // 运算符；如果你想覆盖 class 中的 // 运算符，你需要实现 __floordiv__.
我正在尝试重载 python 中的除法运算符。
class Fraction:
def __init__(self,top,bottom):
def gcd(m, n):
while m % n != 0:
old_m = m
old_n = n
m = old_n
n = old_m % old_n
return n
common = gcd(top,bottom)
self.num = top/common
self.den = bottom/common
def __str__ (self):
return str(self.num) + "/" + str(self.den)
def get_num(self):
return self.num
def get_den(self):
return self.den
def __add__(self, other_fraction):
new_num = self.num * other_fraction.den + self.den * other_fraction.num
new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
def __sub__(self, other_fraction):
new_num = self.num * other_fraction.den - self.den * other_fraction.num
new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
def __mul__ (self, other_fraction):
new_num = self.num * other_fraction.num
new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
def __truediv__(self, other_fraction):
new_num = self.num * other_fraction.den
new_den = self.den * other_fraction.num
return Fraction(new_num, new_den)
def __eq__(self, other):
first_num = self.num * other.den
second_num = other.num * self.den
return first_num == second_num
a = Fraction(10,20)
b = Fraction(30,20)
print a
print "numerator is",a.get_num()
print "denominator is",a.get_den()
print "equality is",(a==b)
print "sum is",(a+b)
print "difference is",(a-b)
print "product is",(a*b)
print "division is",(a/b)
但我在 __truediv__ 处收到错误消息：
TypeError: unsupported operand type(s) for /: 'instance' and 'instance'
代码有什么问题？
object.__truediv__() 特殊方法 仅 与 / 运算符一起使用，然后仅当您将 Python 编译器切换为使用真正的除法：
from __future__ import division
如果您没有使用该导入，/ 运算符会调用 object.__div__() special method（如果存在）。
另一方面，// 运算符调用您未实现的 object.__floordiv__() special method。
来自docs:
object.__div__(self, other) object.__truediv__(self, other)The division operator (/) is implemented by these methods. The
__truediv__()method is used when__future__.divisionis in effect, otherwise__div__()is used. If only one of these two methods is defined, the object will not support division in the alternate context; TypeError will be raised instead.
和here：
A future statement is a directive to the compiler that a particular [python program] should be compiled using syntax or semantics that will be available in a ... future release of Python. The future statement is intended to ease migration to future versions of Python that introduce incompatible changes to the language. It allows use of the new features before the release in which the feature becomes standard.
future_statement: from __future__ import featureThe features recognized by Python 2.x are unicode_literals, print_function, absolute_import, division, generators, nested_scopes and with_statement
现在，一些测试：
~$ python2.7
Python 2.7.6 (v2.7.6:3a1db0d2747e, Nov 10 2013, 00:42:54)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 3/2
1
>>> exit()
~$ python3.2
Python 3.2.3 (v3.2.3:3d0686d90f55, Apr 10 2012, 11:25:50)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 3/2
1.5
所以，你看，/ 运算符的效果在 python 3.x 中发生了变化。您也可以在下面的示例中看到这一点：
class Dog(object):
def __div__(self, other):
print("__div__ called")
def __truediv__(self, other):
print("__truediv__ called")
Dog() / Dog()
--output:--
~/python_programs$ python2.7 myprog.py
__div__ called
~/python_programs$ python3.4 myprog.py
__truediv__ called
因为 __truediv__ 不被 python 2.x 中的 / 运算符调用，覆盖 python [=54= 中的 __truediv__ ] 无效。
PEP 238 - PEP 238 -- Changing the Division Operator
We propose the following transitional measures:
- Classic division will remain the default in the Python 2.x
series; true division will be standard in Python 3.0.
- The // operator will be available to request floor[, i.e. integer,]
division unambiguously.
- The future division statement, spelled "from __future__ import
division", will change the / operator to mean true division
throughout the [program]
现在，看看这里发生了什么：
from __future__ import division
class Dog(object):
def __div__(self, other):
print("__div__ called")
def __truediv__(self, other):
print("__truediv__ called")
Dog() / Dog()
--output:--
~/python_programs$ python2.7 myprog.py
__truediv__ called
~/python_programs$ python3.4 myprog.py
__truediv__ called
现在，您在 python 2.x 中获得 python3.x 运算符的 / 效果。因此，现在您可以覆盖 __truediv__ 以使 / 运算符执行您想要的操作。
注意，如果你想在python3.x中进行整数除法，即3/2 => 1，那么你必须使用//运算符，它由[=实现28=]。同样，如果你在 python 2.x 中执行 from __future__ import division，那么要得到整数除法，你必须使用 // 运算符；如果你想覆盖 class 中的 // 运算符，你需要实现 __floordiv__.