Difference between revisions of "Python-3.4.3/C4/Getting-Started-with-Functions/English"

Objectives

• Define a function
• Define functions with arguments and
• use docstrings.

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3 and
• IPython 5.1.0

Pre-requisite

If not, see the relevant Python tutorials on this website.

Function

• A function is a portion of code within a larger program that performs a specific task.
• Functions are useful in reusing the code and eliminate code redundancy.
• Functions are also used to organise our code into manageable blocks.

Syntax of functions:

def function_name(parameters):"""docstring""" statement(s)

return [expression]

Highlight according to narration

def is the keyword which defines the function name.

colon is used to mark the end of the function name.

docstring is the documentation string to describe what the function does.

It is an optional, but recommended.

Statement makes the function body and it must have 4 indentation level.

return statement is to return a value from the function and it is also indented by 4 spaces.

Example: Function

f(x) a mathematical function

def f(x):

return x*x

Consider a mathematical function f of x is equal to x squared.

Here x is a variable. f of x changes when x changes.

Let us define our function f of x.

The first line def f of x is used to define the function name and its parameters.

The second line uses the function parameters to return the required value.

Open the terminal.

then press Enter

From here onwards, remember to press the Enter key after typing every command on the terminal.

def f(x):

return x*x

def f inside brackets x colon

return x asterisk x

and press the Enter key two times.

f(2)

f(2.5)

Type,

f inside brackets 2

f inside brackets 2.5

It returned 4 and 6.25 respectively.

def greet():

print ("No function arguments")

Type the code as shown.

It defines a new function named greet which will print "No function arguments"

greet()

The function greet neither takes any arguments nor returns any value.

docstrings

Documenting/commenting code is a good practice.

Docstrings are triple quoted comments entered just after the function definition.

It implies what the function does.

""" avg takes two numbers as input a & b. Returns the average of a and b"""

return (a + b) / 2.0

Type the code as shown.

and press the Enter key two times.

Comments within triple quotes give a clear explanation about the code.

avg?

avg question mark

Here we can see the docstring of the function avg.

avg(3, 5)

Type, avg inside brackets 3 comma 5

We get 4.0 as output.

Try this exercise and then resume the video.

Assignment 1

def circle(r):

"""returns area and perimeter of a circle

given radius r"""

pi = 3.14

area = pi * r * r

perimeter = 2 * pi * r return area, perimeter

Press the Enter key two times.

The circle function requires us to return two values.

A python function can return any number of values in the form of a tuple.

a, p = circle(6)

a comma p is equal to circle inside brackets 6

print (a, p)

print inside brackets a comma p

We can see the output as area and perimeter of a circle of radius 6.

Summary

In this tutorial, we have learnt to,

• Define functions in Python
• Call a function by specifying the function name
• Write docstrings to a function by putting it as a triple quoted string
• Pass parameters to a function
• Return values from a function.

Self assessment questions

1. How many arguments can be passed to a Python function?
2. Write a function to find the area of a rectangle.

Solution of self assessment questions

1. Any number of arguments can be passed to a Python function.

1. We can write a function to find the area of a rectangle as:

def rectangle underscore area inside brackets l comma b colon

return l asterisk b

Acknowledgment

http://spoken-tutorial.org

For more details, visit this website.

Thanks for watching.