Python callable

Summary: in this tutorial, you’ll learn about Python callable objects and how to use the callable function to check if an object is callable.

Introduction to Python callables #

When you can call an object using the () operator, that object is callable:

object()Code language: Python (python)

For example, functions and methods are callable. In Python, many other objects are also callable.

A callable always returns a value.

To check if an object is callable, you can use the built-in function callable:

callable(object)Code language: Python (python)

The callable function accepts an object. It returns True if the object is callable. Otherwise, it returns False.

Python callable function examples #

The following illustrates the various types of callable objects in Python.

1) built-in functions #

All built-in functions are callable. For example, print, len, even callable.

print(callable(print))
print(callable(len))
print(callable(callable))Code language: Python (python)

Output:

True
True
True
Code language: PHP (php)

2) User-defined functions #

All user-defined functions created using def or lambda expressions are callable. For example:

def add(a, b):
    return a + b


print(callable(add))  # True
print(callable(lambda x: x*x))  # TrueCode language: Python (python)

Output:

True 
TrueCode language: PHP (php)

3) built-in methods #

The built-in method such as a_str.upper, a_list.append are callable. For example:

str = 'Python Callable'
print(callable(str.upper))  # TrueCode language: Python (python)

Output:

TrueCode language: PHP (php)

4) Classes #

All classes are callable. When you call a class, you get a new instance of the class. For example:

class Counter:
    def __init__(self, start=1):
        self.count = start

    def increase(self):
        self.count += 1

    def value(self):
        return self.countCode language: Python (python)

5) Methods #

Methods are functions bound to an object, therefore, they’re also callable. For example:

print(callable(Counter.increase))  # TrueCode language: Python (python)

Output:

TrueCode language: PHP (php)

6) Instances of a class #

If a class implements the __call__ method, all instances of the class are callable:

class Counter:
    def __init__(self, start=1):
        self.count = start

    def increase(self):
        self.count += 1

    def value(self):
        return self.count

    def __call__(self):
        self.increase()


    counter = Counter()
    counter()

    print(callable(counter))  # TrueCode language: Python (python)

Output:

TrueCode language: PHP (php)

Summary #

• An object is callable when it can be called using the () operator.
• Use the Python callable built-in function to check if an object is callable or not.