FUNCTIONS

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Python - Functions

A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

A function can return data as a result.

Creating a Function :

In Python a function is defined using the def keyword.

def my_function():
  print("Hello from a function")

Calling a function :

To call a function, use the function name followed by parenthesis:

def greet():
    print("hello")
    print("good morning")
greet()

====o/p====
hello
good morning

# another way for running a function :

def greet():
    print("hello")
    print("good morning")
def add(x,y):
    c=x+y
    print(c)
greet()
add(5,4)

=====o/p=====
hello
good morning
9

Parameters :

Information can be passed to functions as parameter.

Parameters are specified after the function name, inside the parentheses. You can add as many parameters as you want, just separate them with a comma.

The following example has a function with one parameter (fname). When the function is called, we pass along a first name, which is used inside the function to print the full name:

def my_function(fname):
  print(fname + " royss")

my_function("sweejana")
my_function("Trishool")
my_function("Laswini")


=====o/p=====

sweejana royss
Trishool royss
Laswini royss

Default Parameter Value :

The following example shows how to use a default parameter value.

If we call the function without parameter, it uses the default value:

def my_function(country = "Norway"):
    print("I am from" + country)
my_function("Sweden")
my_function("India")
my_function()
my_function("Brazil")

=====o/p====

I am from Sweden
I am from India
I am from Norway
I am from Brazil

Passing a List as a Parameter :

We can send any data types of parameter to a function (string, number, list, dictionary etc.), and it will be treated as the same data type inside the function.

E.g. if we send a LIST as a parameter, it will still be a List when it reaches the function.

def my_function(vowels):
    for i in vowels:
        print(i)
vowels=["a","e","i","o","u"]
my_function(vowels)

=====o/p=====
a
e
i
o
u

Return Values :

To let a function return a value, use the 'return' statement.

def my_function(x):
  return 5 * x

print(my_function(3))
print(my_function(5))
print(my_function(9))

====o/p====
15
25
45

Keyword Arguments :

We can also send arguments with the key = value syntax.

This way the order of the arguments does not matter.

def my_function(child3,child2,child1):
    print("The eldest child" + child1)
my_function(child1="srishan",child2="srusti",child3="tanush")

====o/p====
The eldest child srishan 

The phrase Keyword Arguments are often shortened to kwargs in Python documentations.

Arbitrary Arguments :

If we do not know how many arguments that will be passed into function, add '*' before the parameter name in the function definition.

This way the function will receive a tuple of arguments, and can access the items accordingly:

If the number of arguments are unknown, add  '*' before the parameter name :

def my_function(*kids):
    print("the youngest child is" + kids[2])
my_function("srishan","srusti","tanush")

=====o/p====
the youngest child is tanush

The pass Statement :

function definitions cannot be empty, but if we have a function definition with no content for some reason , put in the pass statement to avoid getting an error.

def my_function():
  pass

====o/p====
# it executes without an error

Recursion :

Python also accepts function recursion, which means a defined function can call itself.

Recursion is a common mathematical and programming concept. It means that a function calls itself. This has the benefit of meaning that you can loop through data to reach a result.

The developer should be very careful with recursion as it can be quite easy to slip into writing a function which never terminates, or one that uses excess amounts of memory or processor power. However, when written correctly recursion can be a very efficient and mathematically-elegant approach to programming.

In this example, tri_recursion() is a function that we have defined to call itself ("recurse"). We use the k variable as the data, which decrements (-1) every time we recurse. The recursion ends when the condition is not greater than 0 (i.e. when it is 0).

To a new developer it can take some time to work out how exactly this works, best way to find out is by testing and modifying it.

def tri_recursion(k):
  if(k>0):
    result = k+tri_recursion(k-1)
    print(result)
  else:
    result = 0
  return result

print("\n\nRecursion Example Results")
tri_recursion(6)

=====o/p=====


Recursion Example Results
1
3
6
10
15
21