When Is an Object Callable in Python? A Deep Dive into callable()

What is callable()

Python's built‑in callable() function checks whether an object can be called like a function. It returns True for functions, methods, lambdas, classes, and instances that define a __call__ method; otherwise it returns False. A True result does not guarantee that the call will succeed, but a False result guarantees it will fail.

Syntax

callable(object)

Parameters and Return Value

object – the object to test.

Returns True if the object is callable, otherwise False.

Basic Examples

> callable(0)
False
> callable("runoob")
False
> def add(a, b):
...     return a + b
> callable(add)
True
> class A:
...     def method(self):
...         return 0
> callable(A)
True
> a = A()
> callable(a)
False
> class B:
...     def __call__(self):
...         return 0
> callable(B)
True
> b = B()
> callable(b)
True

Extended Examples

Using help(callable) shows the official documentation.

print(help(callable))
# callable(object) -> bool
# Return whether the object is callable (i.e., some kind of function).
# Note that classes are callable, as are instances with a __call__() method.

Additional demonstrations:

Functions and lambdas are callable:

f = lambda x, y: x + y
f(2, 3)   # 5
callable(f)   # True

Classes are callable, and their methods are callable:

class C:
    def printf(self):
        print('This is class C!')
callable(C)          # True
callable(C.printf)   # True
objC = C()
callable(objC.printf) # True

Instances are callable only if they implement __call__:

class A:
    def printf(self):
        print('This is class A!')
objA = A()
callable(A)   # True
callable(objA)   # False
class B:
    def __call__(self):
        print('This is class B!')
objB = B()
callable(B)   # True
callable(objB)   # True

Built‑in types such as integers, strings, lists, tuples, and dictionaries are not callable:

callable(2)          # False
callable('python')   # False
callable([1,2,3])    # False
callable((4,5,6))    # False
callable({'a':1})    # False