Using Python Properties

In object-oriented programming, you can encounter with the concept of Mutator method where mutator means setter and accessor means getter. Although there is a strong opposition in using such methods for several contexts, for a well-defined mathematical system, getter and setter methods can prevent users making huge computational errors by enabling controlled access and integrated consistency checking.

Python comes with a function named property() which simplifies creating mutator and accessor methods. This function uses Python descriptor protocol to create these methods. @property decorator is a syntactic sugar for the property() function.

NURBS-Python makes use of Python properties to create getter and setter methods. For instance, degree is a Curve class property and it should be used as follows:

from geomdl import NURBS

crv = NURBS.Curve()  # create a NURBS curve instance
crv.degree = 3  # sets curve degree to 3
my_curve_degree = crv.degree  # gets the curve degree and assigns it to a variable
print(my_curve_degree)  # prints "3"

On the other hand, the following use would raise a TypeError exception:

from geomdl import NURBS

crv = NURBS.Curve()  # create a NURBS curve instance
crv.degree(3)  # raises TypeError: 'int' object is not callable
my_curve_degree = crv.degree()  # raises TypeError: 'int' object is not callable

A callable object is a function-like object. Python properties are not functions or methods, although they are defined like them.