Functions Basics

Function is a code block that executes certain task.

Syntax

def funcName(): # Code to execute.

Void Example

A void function doesn't return any value.

Example:

def printHi(): print("Hi!") printHi() # Calling a function:

Output:

Hi!

Returning Result

Via the return keyword a result can be returned.

Let's have an example in which rectangle's area is calculated by passing arguments about it's sides.

Example:

def calcRectangleArea(widthArg, heightArg): return widthArg * heightArg area = calcRectangleArea(3, 4) print(area)

Output:

12

There are couple of things to mark:

• A functions is defined at lines 1 - 2. It accepts two arguments - widthArg and heightArg.
• The function calcRectangleArea returns a result.
• calcRectangleArea is called at line 4.
• It's returned value is set in the variable area.

Not passing argument

If a function requires more arguments than the passed ones, an exception is thrown.

def printArgs(a, b, c): print(a, b, c) printArgs(3, 4)

The function printArgs expects 3 arguments but the last one (c) is not passed. For that reason an exception is thrown.

Default Value

Default value may be specified for function parameters.

Let's look at the following:

def printArg(arg = 3): print(arg) printArg(5) printArg()

Output:

5 3

At line 5 the function argument is not passed thus it takes the default value - 3 specified at line 1.

If arg didn't have default value (3), then the code would result in exception due to line 5.

Call Before Definition

Calling function before it's definition results in exception.

Example:

sayHi() def sayHi(): print("Hi")

The line sayHi() needs to be the last line of the code in order to avoid error.