In Python, functions are a reusable blocks of code that perform a specific task. They allow you to encapsulate logic, promote code reusability, and improve the organization of your code.
The syntax of declaring a function is:
Below is a function with no parameters
def func_name() :
statement_1
statement_2
statement_3
func_name() ## Calling the function
Examples:
Here's a function with parameters that accepts and prints the name entered by the user
def name ( a ) :
print ( a )
name ( input ( " Enter the name " ) )
Here's a function with return value and parameters
def add ( a , b ) :
return a + b
c = add ( 4 , 5 )
print ( c )
Let's look at the various types of functions:
1. Lambda Function ( Single line function )
Below is a function to square a number
x = int ( input ( " Enter a number " ) )
ans = lambda x : x ** 2
print ( ans )
To add two numbers:
x = 5 , y = 10
sum = lambda x , y : x + y
print ( sum )
2. Map Function
It is a higher order function
Syntax -- print ( iterable ( map ( func_name , iterable ) ) )
Example :
To print the square of the elements in the list -
lis = [ 1 , 2 , 3 , 4 ]
def fun ( x ) :
return x **2
print ( list ( map ( fun , lis ) ) )
We can do all this in a single line as follows:
lis = [ 1 , 2 , 3 , 4 ]
print ( list ( map ( lambda x : x ** 2 , lis ) ) )
3. Filter Function
For instance a filter function can be used to filter and separate odd and even numbers from a list as follows
lis = [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ]
odd = list ( filter ( lambda x : x % 2 != 0 , lis ) ) )
even = list ( filter ( lambda x : x % 2 == 0 , lis ) ) )
print ( odd )
print ( even )
4. Reduce Function
The reduce()
function in Python is part of the functools module and is used to perform a
rolling computation on a sequence of elements. It continually applies a
function to pairs of elements from left to right until only a single value
remains.
Example:
To find the sum of elements in a list:
lis = [ 1 , 2 , 3 , 4 , 5 ]
from functools import reduce ## need to import the function
def fun ( x , y ) :
return x + y
print ( reduce ( fun , lis ) )
Recursive functions
A function that calls itself is a recursive function
Example:
Below is a code that finds factorial of a 5 using recursion
def fact ( n ):
if ( n == 0 ):
return 1
else:
return n * factorial ( n - 1 )
print ( fact ( 5 ) )
Output:
120
Doc String
Documenting the purpose of execution of a function
Example:
def square ( n ):
''' Returns square of a number ''' # This is the doc string
return n**2
print ( square.__doc__ )
square ( 2 )
Output:
Returns square of number
4
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