Functions in python3

Syntax of Function
def function_name(arguments):
"""docstring"""
statement(s)
• Keyword def marks the start of function header.
• arguments through which we pass values to a function. They are optional.
• A colon (:) to mark the starting of function
• Optional documentation string (docstring) to describe what the function does.
• One or more valid python statements that make up the function body.
Statements must have same indentation level (usually 4 spaces).
• An optional return statement to return a value from the function.

Defining and Calling Functions
Step 1: Declare the function with the keyword def followed by the function name.
Step 2: Write the arguments inside the opening and closing parentheses of the
function, and end the declaration with a colon.
Step 3: Add the program statements to be executed.
Step 4: End the function with/without return statement.
Ex:
def hello():
print("Hello, World!") #statements inside function
hello() #function calling

Example of Function that takes one string arguments
def greet(name):
"""This function greets to the person passed in as parameter"""
print("Hello, " + name + ". Good morning!")
greet('vani') #function calling
Output:
Hello, vani. Good morning!
print(greet.__doc__)
Output:
This function greets to the person passed into the name parameter

return statement
The return statement is used to exit a function and go back to the place
from where it was called.
the return statement itself is not present inside a function, then the
function will return the None object.
def absolute_value(num):
if num >= 0:
return num
else:
return -num
print(absolute_value(2)) Output: 2
print(absolute_value(-4)) Output: 4

Return multiple values
def add_numbers(x, y, z):
a = x + y
b = x + z
c = y + z
return a, b, c
sums = add_numbers(1, 2, 3)
print(sums)
Output
(3, 4, 5)

Functions exit immediately when they hit a
return statement
def loop_five():
for x in range(0, 25):
print(x)
if x == 5:
# Stop function at x == 5
return
print("This line will not execute.")
loop_five()

Using main() as a Function
def hello():
print("Hello, World!")
def main():
print("This is the main function.")
hello()
main()
Output:
This is the main function.
Hello, World!

def sum():
a=15 #local variable
b=8
print("in fun", a)
sum()
print("outside", a)
$python3 main.py
in fun 15
Traceback (most recent call last): File "main.py", line 8, in <module> print("outside",
a) NameError: name 'a' is not defined
a=15
def sum():
b=8
print("in fun", a)
sum()
print("outside", a)
$python3 main.py
in fun 15
outside 15
a=15
def sum():
a=10
b=8
print("in fun", a)
sum()
print("outside", a)
a=15
def sum():
global a
a=10
b=8
print("in fun", a)
sum()
print("outside", a)
Scope of a Variable: Local and Global Variables

In the next program we’ll declare a global variable and modify our
original names() function so that the instructions are in two discrete
functions.
The first function, has_vowel() will check to see if the name string
contains a vowel.
The second function print_letters() will print each letter of the name
string.

name = str(input('Enter your name: ')) # Declare global variable name for use in all functions
# Define function to check if name contains a vowel
def has_vowel():
if set('aeiou').intersection(name.lower()):
print('Your name contains a vowel.')
else:
print('Your name does not contain a vowel.')
def print_letters(): # Iterate over letters in name string
for letter in name:
print(letter)
def main(): # Define main method that calls other functions
has_vowel()
print_letters()
main() # calling main() function

Four types of function arguments.
• Default Arguments
• Required Arguments
• Keyword Arguments
• Arbitrary Arguments

Default arguments example
Default values indicate that the function argument will take
that value if no argument value is passed during function call.
The default value is assigned by using assignment (=) operator.
Here, msg parameter has a default value Good morning!.
def greet(name, msg = "Good morning!"):
print("Hello",name + ', ' + msg)
greet("Kate")
greet("Bruce","How do you do?")

Required Arguments
Required arguments are the mandatory arguments of a function.
def greet(name,msg):
greet("Monica","Good morning!")
>>> greet("Monica") # only one argument
TypeError: greet() missing 1 required positional argument: 'msg'

Keyword arguments example
The keywords are mentioned during the function call along with their
corresponding values. These keywords are mapped with the function
arguments so the function can easily identify the corresponding values
even if the order is not maintained during the function call.
def greet(name, msg):
greet(msg = "How do you do?",name = "Bruce")

Variable number of arguments example
we can have a design where any number of arguments can be passed based on the
requirement.
def greet(*names):
for name in names:
print("Hello",name)
greet("Monica","Luke","Steve","John")
Output
Hello Monica
Hello Luke
Hello Steve
Hello John

def sum(a,*b):
for i in b:
print(i)
sum(5,6,7.3)
# output:
6
7.3
def person(a,**b):
for i,j in b.items():
print(i,j);
person(5,age=18,mob=9542352)
Output:
age 18
mob 9542352

Functions in python3

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Functions in python3