Use more setters and getters in the Python API

[omichel]

Python users are used to using getters and setters to access properties of objects. See for example #1687. Such getters and setters are not implemented in the Webots Python API. They could be easily added. See https://www.geeksforgeeks.org/getter-and-setter-in-python for reference.

[DavidMansolino]

This is, unfortunately, one more drawback of using Swig, our Python API comes from the C++ one and this is clearly visible (not pythonic at all) :disappointed:

[omichel]

My suggestion is to add (and maintain) python getters and setters in addition to the functions derived from Swig (to keep backwards compatibility).

[lukicdarkoo]

Maybe, this could be a good opportunity to go from camel-case to underscore notation (recommended by PEP 8).

[AhmedMoamen62]

it can be solved by replacing every setter and getter in the code with its structure attribute by a scripting file in webots api layer before generating c++ api with swig, it could be temporary solution to avoid backwards compatibility

[omichel]

@AhmedMoamen62: can you provide a simple example to explain what you mean?

[AhmedMoamen62]

if i understand right, the problem is, camera_recognition_object struct for example

typedef struct {
 int      id;
 double   position[3];
 double   orientation[4];
 double   size[2];
 int      position_on_image[2];
 int      size_on_image[2];
 int      number_of_colors;
 double  *colors;
 char    *model;
} WbCameraRecognitionObject;

and in python we want to access attributes of the struct by setters and getters as

camera_recognition_object.get_id()

instead of

 camera_recognition_object.id

but If you wrap a C structure with SWIG , it is wrapped by a Python class so it will work with just

camera_recognition_object.id 

as in this swig tutorial http://www.swig.org/Doc1.3/Python.html#Python_nn19

so we can write a script to check if python file have any setter or getter function and replace it with the opposite attribute so SWIG can work and compile

[omichel]

OK, I see. But WbCameraRecognitionObject is a special case. In most cases, we have API functions like webots::Camera::getImage() (in C++) which we would like to translate in Python to Camera.image instead of Camera.getImage(). But we would like to keep the later option for backwards compatibility.

[lukicdarkoo]

For conversion from camel-case to underscore notation we can use SWIG regex: http://www.swig.org/Doc2.0/SWIG.html#SWIG_advanced_renaming

For getters and setters, we can implement generating implementation in Python with setattr() and getattr(): https://docs.python.org/3/library/functions.html#setattr

Just ideas, not sure if they are going to work. I can make a minimal proof-of-concept if needed

[omichel]

Yes, if you can quickly make a minimal proof-of-concept, that would be helpful.

[lukicdarkoo]

import re
import random


def add_setter_getters(class_type):
    """Function for adding getters and setters."""

    for full_attr_name in dir(class_type):
        # Find getter and setter methods
        parsed_attr = re.findall(r'^(get|set)([A-Z].*?)$', full_attr_name)
        if parsed_attr:
            # Get relavant data getter and setter methods
            property_suffix = parsed_attr[0][1]
            attr_name = property_suffix.lower()

            # Get set[Something] and get[Something] methods
            fget = None
            fset = None
            if hasattr(class_type, 'get' + property_suffix):
                fget = getattr(class_type, 'get' + property_suffix)
            if hasattr(class_type, 'set' + property_suffix):
                fset = getattr(class_type, 'set' + property_suffix)

            # Create a property
            setattr(class_type, attr_name, property(
                fget=fget,
                fset=fset
            ))


# Our class
class DistanceSensor:
    def __init__(self):
        self.__name = 'distance_sensor'

    def getValue(self):
        return random.randint(1, 100)

    def getName(self):
        return self.__name

    def setName(self, name):
        self.__name = name


# Apply Pythonic setters and getters
add_setter_getters(DistanceSensor)

# Do a few tests
ds = DistanceSensor()
print(ds.value)
print(ds.value)
print(ds.value)
print(ds.name)
ds.name = 'new_distance_sensor'
print(ds.name)

add_setter_getters() is important part that we would put in controller.i, the rest is only for testing purposes. Also, it probably could be simplified.

---

Similar could be done for camel-case to underscore conversion, but that part could be also done with SWIG regex I believe.

[ygoumaz]

Now that we got rid of SWIG, the setters and getters could be implemented more easily.