python - functools.partial on class method -

i'm trying define class methods using more generic class method follows:

class rgb(object):     def __init__(self, red, blue, green):         super(rgb, self).__init__()         self._red = red         self._blue = blue         self._green = green      def _color(self, type):         return getattr(self, type)      red = functools.partial(_color, type='_red')     blue = functools.partial(_color, type='_blue')     green = functools.partial(_color, type='_green') 

but when attempt invoke of methods get:

rgb = rgb(100, 192, 240) print rgb.red() typeerror: _color() takes 2 arguments (1 given) 

i guess self not passed _color since rgb.red(rgb) works.

you creating partials on function, not method. functools.partial() objects not descriptors, not add self argument , cannot act methods themselves. can only wrap bound methods or functions, don't work @ unbound methods. documented:

partial objects function objects in callable, weak referencable, , can have attributes. there important differences. instance, __name__ , __doc__ attributes not created automatically. also, partial objects defined in classes behave static methods , not transform bound methods during instance attribute look-up.

use propertys instead; these are descriptors:

class rgb(object):     def __init__(self, red, blue, green):         super(rgb, self).__init__()         self._red = red         self._blue = blue         self._green = green      def _color(self, type):         return getattr(self, type)      @property     def red(self): return self._color('_red')     @property     def blue(self): return self._color('_blue')     @property     def green(self): return self._color('_green') 

as of python 3.4, can use new functools.partialmethod() object here; it'll right thing when bound instance:

class rgb(object):     def __init__(self, red, blue, green):         super(rgb, self).__init__()         self._red = red         self._blue = blue         self._green = green      def _color(self, type):         return getattr(self, type)      red = functools.partialmethod(_color, type='_red')     blue = functools.partialmethod(_color, type='_blue')     green = functools.partialmethod(_color, type='_green') 

but these'd have called, whilst property objects can used simple attributes.