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
"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.
"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 1return n * factorial(n - 1)# Example usageprint(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 Falsefor i in range(2, int(num**0.5) + 1):if num % i == 0:return Falsereturn True# Example usageprint(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 Nonelargest = numbers[0]for num in numbers:if num > largest:largest = numreturn largest# Example usageprint(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 usageprint(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 usagestring_permutations("abc")
# Output:abcacbbacbcacabcba
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 usageprint(fibonacci(10))
# Output: [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
