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What is a callable object in Python? |
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Answer» An object that can invoke a certain action or process is callable. The most obvious example is a function. Any function, built-in or user defined or a method in built-in or user defined class is an object of Function class >>> def myfunction(): print ('HELLO') >>> type(myfunction) <class 'function'> >>> type(print) <class 'builtin_function_or_method'>Python’s standard library has a nuilt-in callable() function that returns true if object is callable. Obviously a function returns true. >>> callable(myfunction) True >>> callable(print) TrueA callable object with parentheses (having arguments or not) invokes associated functionality. In fact any object that has access to __call__() MAGIC method is callable. Above function is normally called by entering myfunction(). However it can also be called by using __call_() method inherited from function class >>> myfunction.__call__() Hello >>> myfunction() HelloNumbers, string, collection objects etc are not callable because they do not inherit __call__() method >>> a=10 >>> b='hello' >>> c=[1,2,3] >>> callable(10) False >>> callable(b) False >>> callable(c) FalseIn Python, class is also an object and it is callable. >>> class MyClass: def __init__(SELF): print ('called') >>> MyClass() called <__main__.MyClass object at 0x7f37d8066080> >>> MyClass.__call__() called<__main__.MyClass object at 0x7f37dbd35710> However, object of MyClass is not callable. >>> m=MyClass() called >>> m() Traceback (most recent call last): File "<pyshell#23>", LINE 1, in <module> m() TypeError: 'MyClass' object is not callableIn order that object of user defined be callable, it must override __call__() method >>> class MyClass: def __init__(self): print ('called') def __call__(self): print ('this makes object callable') >>> m=MyClass() called >>> m() this makes object callable |
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