Defining Functions In Python

A function, once defined, can be invoked as many times as needed by using its name, without having to rewrite its code.

A function in Python is defined as per the following syntax:

def​ <​function​-​name​>(<parameters>):
    """ Function's docstring """ 
    <Expressions/Statements/Instructions>

● Function blocks begin with the keyword def​ followed by the function name and ​parentheses​ ( ( ) ).

● The input parameters​ or ​arguments​ should be placed within these parentheses. You can also define parameters inside these parentheses.

● The first statement of a function is optional - the documentation string of the function or ​docstring.​ The docstring​ describes the functionality of a function.

● The code block within every function starts with a colon ​(:) and is indented.​ All statements within the same code block are at the same indentation level.

● The ​return​ statement exits a function, optionally passing back an expression/value to the function caller.

Example:

Let us define a function to add two numbers.

def add(a,b):
    
    return a + b

Output:

The above function returns the sum of two numbers ​a​ and ​b​.

In the example given above, the sum a​ +b​ is returned.

Note:​ In Python, you need not specify the return type i.e. the data type of returned

value

Calling/Invoking A Function

Once you have defined a function, you can call it from another function, program, or even the Python prompt. To use a function that has been defined earlier, you need to write a function call​.

A function call​ takes the following form:

<function-name> (<value-to-be-passed-​as​-argument>)

The function definition does not execute the function body. The function gets executed only when it is called or invoked. To call the above function we can write:

add(​5​,​7​)

In this function call, a​ = ​5​ and ​b = ​7​.

Arguments And Parameters

As you know that you can pass values to functions. For this, you define variables to receive values in the function definition​ and you send values via a function call statement. For example, in the ​add()​ function, we have variables ​a​ and ​b​ to receive the values and while calling the function we pass the values 5 and 7. We can define these two types of values:

 ●  Arguments:​ The values being passed to the function from the function call statement are called arguments. Eg. ​5​ and ​7​ are arguments to the ​add() function.

●  Parameters: The values received by the function as inputs are called parameters. Eg. a​ and b​ are the parameters of the​  a​dd()​ function.