Python class __call__ method and dot notation-CodePudding

My Goal is to use dot notation to select strings from dictionarys using the SimpleNamespace modeule while having the ability to change which dictionary to use.

To do this i have tried modifying the class __call__ method to change the output based on a previously set variable. However, due to the use of the __call__ method it requires the use of () to be included which breaks the simple formatting of dot notation. Additinally i need to be able to use class methods as well to change the option i am looking for.

class i: x, y = 1, 2
class j: x, y = 3, 4
class myClass:
    def __init__(self):
        self.a, self.b = i(), j()
        self.selection = "a"
    def set_selection(self, selection):
        self.selection = selection
    def __call__(self):
        return getattr(self, self.selection)

mc = myClass()
print(mc().x) ## this generates the output i am wanting by using the __call__ method
mc.set_selection("b") ## i still need to call class methods
print(mc().x)
print(mc.x) ## this is the syntax i am trying to achive

although mc().x works it is not dot notation.

The output i am looking for in this example would be similar to:

import myClass
data = myCalss()

print(data.x   data.y) 
#>>> 3
data.set_selection("b")
print(data.x   data.y) 
#>>> 7

CodePudding user response：

Seem like __call__() is the wrong choice for the interface you want. Instead, maybe __getattr__() is what you want:

class i: x, y = 1, 2
class j: x, y = 3, 4
    
class myClass:
    def __init__(self):
        self.a, self.b = i(), j()
        self.selection = "a"
        
    def set_selection(self, selection):
        self.selection = selection
        
    def __getattr__(self, at):
        return getattr(getattr(self, self.selection), at)

data = myClass()

print(data.x   data.y)
# 3
data.set_selection("b")
print(data.x   data.y) 
# 7

Might want some checks to make sure the selection is valid.

Also, probably worth reading up on descriptors if you will be exploring this kind of stuff more deeply.