Calling Functions in Python

Calling Functions in Python

After writing a function, it’s defined, not executed. To execute we should call it explicitly. The function runs after having been executed. A part of a program that is calling our function is named a caller. Of course, to execute a function and run, we write its name with parentheses accepting a list of arguments.

function_name(arguments_list)

Defining the function sum():

def sum(a,b,c):
    return a+b+c

Calling the function sum():

>>>sum(23,56,89)
168

During execution, a calling program is stopped and waiting for the moment when our function finishes its work, and the control comes back to the caller again.

Defining the first function printing “Hello!”:

def druk():
    print(“Hello!”)

Defining the second function calling the function druk():

def drul():
   druk()

The function drul() is the caller for the function druk(). Let’s call drul():

>>> drul()
Hello!
>>>

Or we can write in other order:

def drul():
   druk()

def druk():
    print(“Hello!”)

We get the same:

>>> drul()
Hello!
>>>

Even if there aren’t any arguments, we must use parentheses with the name of our function to execute it. In this case, they will be empty. A function must be defined before its calling. But we can refer to a function before its defining.

We can check if an object is callable using the built function callable():

callable(object)

>>>callable(print)
True

The function returns True if the object is callable or False if the object isn’t callable. It is in Python 3.x.x because in Python 2.x.x the function callable returns 1 (True) or 0 (False).

Callable objects in Python:

— functions built-in

— functions defined by a user

— methods of built-in objects

— class objects

— class methods

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