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
0c.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