__call__

We have two example below to understand __call__ method - 

1- We are creating lets say an instance of a device which is in active passive and one of the device is active at a time, so we can initialise the class with active ip address and later we can change the ip which is active at that time 

class Device:

def __init__(self, ipaddress):

print(f"__init__ with {ipaddress}")

self.ipaddress = ipaddress

def __call__(self, ipaddress):

print(f"__call__ with {ipaddress}")

self.ipaddress = ipaddress

@property

def getname(self):

return self.ipaddress

if __name__ == "__main__":

x = Device("192.168.120.10")

print(x.getname)

x("192.168.120.20")

print(x.getname)

x("192.168.120.30")

print(x.getname)

##Output

$ python3 callDemo.py __init__ with 192.168.120.10 192.168.120.10 __call__ with 192.168.120.20 192.168.120.20 __call__ with 192.168.120.30 192.168.120.30

2- Maintaining a simple Cache using __call_method

class Example(object):

def __init__(self):

self.factorial = {}



def __call__(self, value):

if value not in self.factorial.keys():

print "calling factorial method"            

self.factorial[value] =  self.fact(value)

return self.factorial[value]

def fact(self, number):

if number == 1:

return 1        

else:

return number * self.fact(number-1)

if __name__ == "__main__":

e = Example()

print e(3)

print e(4)

print e(5)

print e(3)



##Output