Python magic methods (2) : __call__()
In Python, we can call a method using object.method(). Is it possible if we use object() to call a method or do something? __call__() method can help us to achieve this - by defining __call__(), the class’s instance can be called as a function.
Example:
class Person(object):
def __init__(self, name):
self.name = name
def __call__(self):
print('Name is %s.' % self.name)
if __name__ == '__main__':
p = Person('mike')
print p()
Result:
Name is mike.
When to use __call__()?
If we need the objects to be callable, or the object wraps, abstracts the concept of a function, then use __call__().
Example:
class Factorial:
def __init__( self ):
self .cache = {}
def __call__( self , n):
if n not in self .cache:
if n == 0:
self .cache[n] = 1
else:
self .cache[n] = n * self .__call__(n-1)
return self .cache[n]
fact = Factorial()
for i in xrange(10):
print ( "{}! = {}" .format(i, fact(i)))
Result:
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
