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Functions
In Python, a function can be defined as a named block of code. We use
functions mainly to avoid code repetition. We can define that action only once
using a function and call that function whenever required to do the same
activity.
The benefit of using a function is code reusability and modularity. Function
improves efficiency and reduces errors because of the reusability of a code.
Once we create a function, we can call it anywhere and anytime.
Creating a Function
In Python a function is defined using the def keyword. The “def” stands for
define. It is used for telling the interpreter that it is a user defined function. The
“def” is followed by function name, which is followed by parameters(Optional).
Define the function body with a block of code.
Syntax:
functionNameHere(parameters):
def
#your code here

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Note: There is no need to specify curly braces for the function body, in python.
Only indentation is needed to separate code blocks.
Calling a Function
To call a function, use the function name followed by parenthesis, which is
followed by arguments (if any).
:
Note function definitions cannot be empty, but if you for some reason have a
function definition with no content, put in the pass statement to avoid getting
an error.
Arguments

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Arguments are specified after the function name, inside the parentheses, for
passing information into function. You can add as many arguments as you
want, just separate them with a comma.
Parameters and Arguments
1. A parameter is the variable listed inside the parentheses in the function
definition.
2. An argument is the value that is sent to the function when it is called.
Recursion
Recursion means that a defined function calls itself. When written correctly
recursion can be a very useful and effective.

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Example:
#Recursion function which prints upto 99 without for/while
recur (k):
def
if(k <100):
(k)
print
k+=1
( k )
recur
#calling recur
recur (1)
Function Assignment
We can assign a function to a variable in the same way as we assign a value
to it. You can even use those variables to call the function as well.
def proc():
return "Welcome"
procAlias= proc
print(proc)
print(procAlias)
print(proc ())

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print(procAlias())
Return in Function
Return means the task is completed and now you need to return to where you
came, with the specified data. You can return any type of data, you can even
return a function. This should be the last statement in a function.
def proc():
return "Bon Voyage"
print(proc ())
Inner Function
A function which is defined inside another function is known as inner function or
nested function. Nested functions are able to access variables of the enclosing
scope.
Types of function arguments.
There are various ways to use arguments in a function. In Python, we have the
following 4 types of function arguments.

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1. Default argument
2. Keyword arguments (named arguments)
3. Positional arguments
4. Arbitrary arguments (variable-length arguments *args and **kwargs)

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Default Arguments
Default arguments are arguments those have default values. We assign
default values to the argument using the ‘=’ (assignment) operator at the time
of function definition. You can define a function with any number of default
arguments.
The default value of an argument will be used inside a function if we do not
pass a value to that argument at the time of the function call. Due to this, the
default arguments become optional during the function call.
It overrides the default value if we provide a value to the default arguments
during function calls.
Keyword Arguments

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Usually, at the time of the function call, values get assigned to the arguments
according to their position. So we must pass values in the same sequence
defined in a function definition.
For example, when we call show('dass', 19), the value “dass” gets assigned to
the argument name, and similarly, 19 to age and so on as per the sequence.
We can alter this behavior using a keyword argument.
Keyword arguments are those arguments where values get assigned to the
arguments by their keyword (name) when the function is called. It is preceded
by the variable name and an (=) assignment operator. The Keyword Argument
is also called a named argument.
Change the sequence of keyword arguments
Also, you can change the sequence of keyword arguments by using their name
in function calls.
Python allows functions to be called using keyword arguments. But all the
keyword arguments should match the parameters in the function definition.
When we call functions in this way, the order (position) of the arguments can
be changed.
Positional Arguments
Positional arguments are arguments that can be called by their position in the
function definition
By default, Python functions are called using the positional arguments.
Variable-length arguments

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We use variable-length arguments if we don’t know the number of arguments
needed for the function in advance.
Types of Arbitrary Arguments:
 arbitrary positional arguments (*args)
 arbitrary keyword arguments (**kwargs)
The *args and **kwargs allow you to pass multiple positional arguments or
keyword arguments to a function.
Arbitrary positional arguments (*args)
We can declare a variable-length argument with the * (asterisk) symbol. Place
an asterisk (*) before a parameter in the function definition to define an
arbitrary positional argument.
we can pass multiple arguments to the function. Internally all these values are
represented in the form of a tuple.

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