I need to make an operators to an object and I wonder what is the best way.
for example for the operator add
can I write this in this way?
def _add_(self,other):
new=self.add(self,other)// can I write like that?
return new
thanks for the help!
You would use the python magic function __add__ to take care of the +:
Example:
class A():
def __init__(self, num):
self.num = num
def __add__(self, other):
return self.num + other
a = A(6)
>>> print a+5
11
For greater flexibility, you should also define __radd__, this is for the reverse addition case 5+a which would not work in the example above.
class A():
def __init__(self, num):
self.num = num
def __add__(self, other):
return self.num + other
def __radd__(self, other):
return self.num + other
>>> a = A(6)
>>> print 5+a
11
>>> print a+5
11
Or if you want to return as an object instead of an int, you can do it as:
class A():
def __init__(self, num):
self.num = num
def __add__(self, other):
return A(self.num + other)
a = A(5)
b = a+5
print b.num
10
print a.num
5
What has been demonstrated above is operator overloading. It overrides the built-in default methods for handling operators by letting the user define custom methods for the operators.
Here is a list you might find useful as to which operators can be overloaded
b = a + 5, should b be an int or an instance of class A? I vote for the latter.
__iadd__ (self.num += is appropriate for it). Returning int instead of A type makes a + 6 + 1 different from a + 7 (due to side-effects) that is not intuitive.
addto__add__and use__add__everywhere instead ofadd? It will save you one function call, and there will be less duplication.self.add(self,other)seems to contain oneselfmore than needed...self.addreturn?