Ruggero Turra Ruggero Turra - 6 days ago 6
Python Question

Automatic transformation from getter/setter to properties

I have a big library written in C++ and someone created an interface to use it in python (2.6) in an automatic way. Now I have a lot of classes with getter and setter methods. Really: I hate them.

I want to re-implement the classes with a more pythonic interface using properties. The problem is that every class has hundreds of getters and setters and I have a lot of classes. How can I automatically create properties?

For example, if I have a class called

MyClass
with a
GetX()
and
SetX(x)
,
GetY
,
SetY
, etc... methods, how can I automatically create a derived class
MyPythonicClass
with the property
X
(readable if there is the getter and writable if there is the setter), and so on? I would like a mechanism that lets me to choose to skip some getter/setter couples where it is better to do the work by hand.

Answer

Here's a way to do it with a class decorator

def make_properties(c):
    from collections import defaultdict
    props=defaultdict(dict)
    for k,v in vars(c).items():
        if k.startswith("Get"):
            props[k[3:]]['getter']=v
        if k.startswith("Set"):
            props[k[3:]]['setter']=v
    for k,v in props.items():
        setattr(c,k,property(v.get('getter'),v.get('setter')))
    return c

@make_properties
class C(object):
    def GetX(self):
        print "GetX"
        return self._x

    def SetX(self, value):
        print "SetX"
        self._x = value

c=C()
c.X=5
c.X

Here is a slightly more complicated version that allows you to specify a list of items to skip

def make_properties(skip=None):
    if skip is None:
        skip=[]
    def f(c):
        from collections import defaultdict
        props=defaultdict(dict)
        for k,v in vars(c).items():
            if k.startswith("Get"):
                props[k[3:]]['getter']=v
            if k.startswith("Set"):
                props[k[3:]]['setter']=v
        for k,v in props.items():
            if k in skip:
                continue
            setattr(c,k,property(v.get('getter'),v.get('setter')))
        return c
    return f

@make_properties(skip=['Y'])
class C(object):
    def GetX(self):
        print "GetX"
        return self._x

    def SetX(self, value):
        print "SetX"
        self._x = value

    def GetY(self):
        print "GetY"
        return self._y

    def SetY(self, value):
        print "SetY"
        self._y = value

c=C()
c.X=5
c.X
c.Y=5
c.Y
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