Hi,
I'd like to write some class that can help me build reusable formula
easily, some simple code like this.
# -*- coding: utf8 -*-
class OperationResult:
def __init__(self, left, right):
self.dataSource = dataSource
def __add__(self, other):
self.dataSource.stack.append('+')
return self
def __div__(self, other):
self.dataSource.stack.append('/')
return self
class Operand:
def __init__(self, dataSource, name):
self.dataSource = dataSource
self.name = name
def __add__(self, other):
self.dataSource.stack.append(self)
self.dataSource.stack.append(other)
self.dataSource.stack.append('+')
return OperationResult(self.dataSource)
class DataSource:
def __init__(self):
self.stack = []
def __getitem__(self, key):
return Operand(self, key)
def ROE(dataSource):
a = dataSource[u'股東權益總額']
b = dataSource[u'每股淨額']
c = dataSource[u'當季平均市價']
return (a + b) / c
Now I can use ROE formula easily, it will return a object that contain
formula stack like this
[a, b, +, c, /]
And then I can get real data of those items from database or other
place. The formula depends on nothing. It don't care where to get data
and how to calculate it. I can reuse it easily.
Now, here comes the problem : I have to override all the operation
methods, such as __add__ and __mul__.
I know the most stupid way is just to write all of them like this.
def __add__(self, other):
self.leftOperation('add', other)
def __mul__(self, other):
self.leftOperation('mul', other)
But I don't want to do that in this stupid way. I want to use little
code to redirect these operation methods to some specific method with
it's name.
What can I do?
Thanks.
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