Python Functions

Function Definition: Function is a group of statements which performs a specific task. It is also known as a Sub-routine or a Procedure or a Method.

In most programming languages two types of functions available:

• Library Functions (also known as System defined function, for example print(), input(), etc.)
• User defined functions (written by programmers, for example calculate(), find_area(), etc.)

Let's learn how Python Functions works.

Defining a Python Function

Following simple rules are followed while defining Python Functions:

• Function blocks begin with the def keyword; followed by the function name and parentheses (  ).
• Any number of parameters or arguments can be placed within function parentheses.
• In the beginning of functions, writing a short comments about a function is one of the standard practice. 
• Function code begins with a colon(:) and has indentation.
• return statement at the end indicates end of function.

Syntax of Python Function

def function_name( arguments ):
   "function comments"
   function logic / code
   return

By default, arguments or parameters have a positional behavior and you need to write in the same order as they defined.

Python Function Example

The following python function prints line with a specified character as an parameter.

def print_line( chr ):
   "This function prints a line of given character"
   for i in range(0,15)
      print (chr)
   return

print_line('*')

print("")

print(" Welcome to Python Practicals ")

print_line('=')

Output of program

* * * * * * * * * * * * * * * 

 Welcome to Python Practicals 

= = = = = = = = = = = = = = = 

Examples of Popular Python Functions

1. Calculate Factorial

def factorial(n):

    """Calculate the factorial of a number."""

    if n == 0 or n == 1:

        return 1

    return n * factorial(n - 1)

# Example usage

print(factorial(5))  # Output: 120

2. Check if a Number is Prime

def is_prime(num):

    """Check if a number is prime."""

    if num <= 1:

        return False

    for i in range(2, int(num**0.5) + 1):

        if num % i == 0:

            return False

    return True

# Example usage

print(is_prime(7))  # Output: True

3. Find the Largest Element in a List

def find_largest(numbers):

    """Return the largest number in a list."""

    if not numbers:

        return None

    largest = numbers[0]

    for num in numbers:

        if num > largest:

            largest = num

    return largest

# Example usage

print(find_largest([3, 7, 2, 8, 5])) 

# Output: 8

4. Reverse a String

def reverse_string(s):

    """Reverse a given string."""

    return s[::-1]

# Example usage

print(reverse_string("hello"))  

# Output: 

"olleh"

5. Generate all permutations of a string using recursion

def string_permutations(s, prefix=""):

    """Generate all permutations of a string recursively."""

    if len(s) == 0:

        print(prefix)

    else:

        for i in range(len(s)):

            rem = s[:i] + s[i+1:]

            string_permutations(rem, prefix + s[i])

# Example usage

string_permutations("abc")   

# Output:

 abc

 acb

 bac

 bca

 cab

 cba

6. Fibonacci Sequence Generator

def fibonacci(n):

    """Generate a Fibonacci sequence up to n terms."""

    fib_sequence = [0, 1]

    for i in range(2, n):

        fib_sequence.append(fib_sequence[i - 1] + fib_sequence[i - 2])

    return fib_sequence[:n]

# Example usage

print(fibonacci(10)) 

 

# Output: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

* * * * *

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