Redundant Function Call for Decorators in Python

Question

So I was looking at a certain class which has the following property function. However, the property method itself doesn't describe the procedure but instead calls another function to do so as follows:

class Foo():

 @property
 def params(self):
     return self._params()

 @property
 def target(self):
     return self._target()

 def _params(self):
     return print("hello")
 def _target(self):
     return print("world")

What I am trying to understand if it is some sort of pattern? I have seen a similar thing in another class as well where the method with property decorator simply calls another method of same name with underscore in the beginning. Note: I do know what is property decorator but don't understand why this specific way of underscoring aims to achieve.

try this https://stackoverflow.com/questions/17330160/how-does-the-property-decorator-work — hazirovich, Nov 24 '19 at 16:16
I sometimes uses that if for example `_params` takes a few parameters. I would call it `params` and the property would be a shortcut to the default arguments call. — Cedric H., Dec 15 '19 at 10:38
@CedricH. What is the reason for doing so why not simply use params instead of creating another function _params as params is already declared as a property? — gfdsal, Dec 15 '19 at 10:42
@GENIVI-LEARNER Something like this : create a function `get_information` with parameters with default values, then create a property `information` which calls `get_information` with the default set of parameters. This way users of the class have a shortcut and a better look and feel in some cases. In your specific case, has `_params` and `_target` do not take parameters, I do not see the point. — Cedric H., Dec 16 '19 at 11:04
@CedricH.Please elaborate I didnt understand how users of the class have a shortcut and better look and feel. Assuming _params and _target take parameters, how shall it be a shortcut? — gfdsal, Dec 16 '19 at 11:43

score 1 · Accepted Answer · answered Dec 18 '19 at 22:58

1

Effectively, the property is being used as a shortcut for calling a method with a fixed set of arguments. As a slightly different example, consider

class Foo():

    @property
    def params(self):
        return self._params(1, "foo", True)

    def _params(self, x, y, z):
        ...

f = Foo()

Now, f.params is a shortcut for f._params(1, "foo", True). Whether that is worth doing depends on whether _params is used for anything other than implementing the body of the params getter. If it isn't, there's little real point in writing code like this.

answered Dec 18 '19 at 22:58

chepner

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I kinda got it so essentially instead of writing ```f._params(1, "foo", True)``` we can simply do a shortcut such as ```f.params``` without having to specify additional arguments. Right? – gfdsal Dec 19 '19 at 11:24
Also could you please elaborate this: **```_params``` is used for anything other than implementing the body of the params getter** – gfdsal Dec 19 '19 at 11:25
If the sole purpose of defining `_params` is so that you can call it once from the body of `params`, then you should probably just put its code in `params` directly and not define `_params` in the first place. That would save an unnecessary function call. – chepner Dec 19 '19 at 12:52

Redundant Function Call for Decorators in Python

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