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Understanding Python Properties

PROPERTIES:

Properties is a class for managing class attributes in Python. Property( )is a built-in function that creates and returns a property object

Syntax:

attribute_name =property(get_Attribute, set_Attribute, del_Attribute(Optional), doc_Attribue(Optional))

where, get_Attritube is function to get value of the attribute,

set_Attribute is function to set value of the attribute,

del_Attribute is function to delete the attribute and

doc_Attribute is a string (like a comment).

Example:

class Celsius:
    def __init__(self, temperature = 0):
        self.temperature = temperature
    def fahrenheit(self):
        return (self.temperature * 1.8) + 32
    def get_temperature(self):
        print("Getting value")
        return self._temperature
    def set_temperature(self, value):
        print("Setting value")
        self._temperature = value
temperature = property(get_temperature,set_temperature)

Here temperature is the property object. property attaches code (get_temperature and set_temperature) to the attribute (temperature). Any code that retrieves the value of temperature will automatically call get_temperature( ). Similarly, any code that assigns a value to temperature will automatically call set_temperature( ).

Example:

>>>c = Celsius( )

Getting value

Here set_temperature( ) was called even when we created an object. The reason is that when an object is created, __init__ method gets called. This method has the line self.temperature = temperature. This assignment called set_temperature( ).

>>>c.temperature
Getting value
0

c.temperature calls get_temperature()

The actual temperature value is stored in the private variable temperature. The attribute temperature is a property object which provides interface to this private variable.

We can use the property with decorators also, Here we are not defining names get_temperature and set_temperature to pollute the class namespace. For this, we reuse the name temperature while defining our getter and setter functions. we can re-write the above example:

class Celsius:
    def __init__(self, temperature = 0):
        self.temperature = temperature
    def fahrenheit(self):
        return (self.temperature * 1.8) + 32
    @property
    def temperature(self):
        print("Getting value")
        return self._temperature
    @temperature.setter
    def temperature(self, value):
        print("Setting value")
        self._temperature = value
About Micropyramid

Micropyramid is a software development and cloud consulting partner for enterprise businesses across the world. We work on python, Django, Salesforce, Angular, Reactjs, React Native, MySQL, PostgreSQL, Docker, Linux, Ansible, git, amazon web services. We are Amazon and salesforce consulting partner with 5 years of cloud architect experience. We develop e-commerce, retail, banking, machine learning, CMS, CRM web and mobile applications.


Posted On 23 August 2011 By MicroPyramid


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