{"id":1063,"date":"2020-11-12T02:12:13","date_gmt":"2020-11-12T02:12:13","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=1063"},"modified":"2020-11-12T02:15:46","modified_gmt":"2020-11-12T02:15:46","slug":"python-callable","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-built-in-functions\/python-callable\/","title":{"rendered":"Python callable"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about Python callable objects and how to use the callable<\/code> function to check if an object is callable.<\/p>\n\n\n\n

Introduction to Python callables #<\/a><\/h2>\n\n\n\n

When you can call an object using the ()<\/code> operator, that object is callable:<\/p>\n\n\n

object()<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
A callable always returns a value.<\/p>\n\n\n\n
To check if an object is callable, you can use the built-in function callable<\/code>:<\/p>\n\n\n
callable(object)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The callable<\/code> function accepts an object. It returns True<\/code> if the object is callable. Otherwise, it returns False<\/code>.<\/p>\n\n\n\n
Python callable function examples #<\/a><\/h2>\n\n\n\n
The following illustrates the various types of callable objects in Python.<\/p>\n\n\n\n
1) built-in functions #<\/a><\/h3>\n\n\n\n
All built-in functions are callable. For example, print<\/code>, len<\/code>, even callable<\/code>.<\/p>\n\n\n
print(callable(print<\/span>))\nprint(callable(len))\nprint(callable(callable))<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span>\nTrue<\/span>\nTrue<\/span>\n<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
2) User-defined functions #<\/a><\/h3>\n\n\n\n
All user-defined functions created using def<\/code> or lambda<\/code> expressions are callable. For example:<\/p>\n\n\n
def<\/span> add<\/span>(a, b)<\/span>:<\/span>\n    return<\/span> a + b\n\n\nprint(callable(add))  # True<\/span>\nprint(callable(lambda<\/span> x: x*x))  # True<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span> \nTrue<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
3) built-in methods #<\/a><\/h3>\n\n\n\n
The built-in method such as a_str.upper<\/code>, a_list.append<\/code> are callable. For example:<\/p>\n\n\n
str = 'Python Callable'<\/span>\nprint(callable(str.upper))  # True<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
4) Classes #<\/a><\/h3>\n\n\n\n
All classes are callable. When you call a class, you get a new instance of the class. For example:<\/p>\n\n\n
class<\/span> Counter<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, start=1<\/span>)<\/span>:<\/span>\n        self.count = start\n\n    def<\/span> increase<\/span>(self)<\/span>:<\/span>\n        self.count += 1<\/span>\n\n    def<\/span> value<\/span>(self)<\/span>:<\/span>\n        return<\/span> self.count<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
5) Methods #<\/a><\/h3>\n\n\n\n
Methods are functions bound to an object, therefore, they’re also callable. For example:<\/p>\n\n\n
print(callable(Counter.increase))  # True<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
6) Instances of a class #<\/a><\/h3>\n\n\n\n
If a class implements the __call__<\/code> method, all instances of the class are callable:<\/p>\n\n\n
class<\/span> Counter<\/span>:<\/span>\n    def<\/span> __init__<\/span>(self, start=1<\/span>)<\/span>:<\/span>\n        self.count = start\n\n    def<\/span> increase<\/span>(self)<\/span>:<\/span>\n        self.count += 1<\/span>\n\n    def<\/span> value<\/span>(self)<\/span>:<\/span>\n        return<\/span> self.count\n\n    def<\/span> __call__<\/span>(self)<\/span>:<\/span>\n        self.increase()\n\n\n    counter = Counter()\n    counter()\n\n    print(callable(counter))  # True<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
True<\/span><\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
  • An object is callable when it can be called using the ()<\/code> operator.<\/li>
  • Use the Python callable<\/code> built-in function to check if an object is callable or not.<\/li><\/ul>\n
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For example, functions<\/a> and methods are callable. In Python, many other objects are also callable. <\/p>\n\n\n\n