callable() function in Python

Introduction

The callable() method returns True if the object passed to it appears to be callable, else it returns False. Callable means something that can be called.

The syntax of callable() method is:

callable(object)

The callable() method takes a single parameter object and can return one of the two possible values:

True if the object appears to be callable
False if the object doesn't appear to be callable

Note: In some cases, callable() returns True, but the call to the object can still fail. However, if the callable() method returns False, the call to the object will definitely fail.

Example 1

def my_func():
    print("I am a function, I can be called!")


func = my_func
print(callable(func))

my_var = 20
print(callable(my_var))

Output:

True
False

In the first case, an object func of the my_func function is created and passed to the callable() method which appears to be callable. Hence it returns True. However, in the second case, an object my_var is passed which is definitely not callable. Hence, it returns False.

Example 2

The callable() method checks if the argument is either of the following:

an instance of class with a call method
of a type that indicates callability such as method or function

class TestClass1:
    def __call__(self):
        print("Test Class 1 called")

obj1 = TestClass1()
print(callable(obj1))
obj1()

Output:

True
Test Class 1 called

In the above example, the TestClass1 has __call__ method implemented, and hence appears to be callable, and is callable.

class TestClass2:
    def my_method(self):
        print("Test Class 2 called")

obj2 = TestClass2()
print(callable(obj2))
obj2()

Output:

False
Traceback (most recent call last):
  File "D:\Quarantine\Test\Blog-Codes\Built-Ins\callable\ex2.py", line 17, in <module>
    obj2()
TypeError: 'TestClass2' object is not callable

However, in the above example, the TestClass2 appears to be callable, but the instance of the class is not callable, and hence an error is thrown.