PYTHON PROGRAMMING

SYED JANI BASHA

CONTENTS

• PYTHON INTRODUCTION

• FEATURES OF PYTHON

• WHERE WE USE PYTHON

• HISTORY OF PYTHON

• SETTING UP PYTHON

ENVIRONMENT

• PROGRAM DEVELOPMENT CYCLE

• INPUT PROCESSING OUTPUT

Python is the world's most popular and fastest-growing computer

programming language. It is a multi-purpose and high-level programming

language. Python was invented by Guido Van Rossum in the year 1989, but it

was introduced into the market on 20th February 1991.

INTRODUCTION

Python Features

• Python is easy to learn and easy to understand.

• The Python is an interpreted programming

language. It executes the code line by line.

• The Python is a cross-platform programming

language. It can be used with any operating system

like Windows, Linux, MAC OS, etc.

• The Python is a free and open-source programming

language.

• The Python is an Object-Oriented, Procedural and

Functional programming language

• The Python is a multi-purpose programming

language

• The Python is a high-level programming language

• Python has a huge Community to get help all over

the globe.

• Python has a large Ecosystem of Libraries,

Frameworks, and Tools to work with it.

Cont………

Where we use the Python

• Data analysis

• Artificial intelligence / Machine learning

• Mobile Apps

• Desktop Apps

• Web Apps

• Automation

• Hacking

• Testing and more...

History of the Python

Latest version available is 3.8.5

Setting up Python Environment

In the above screen click on the Download Python 3.7.3 to start downloading

the installer for Windows operating system.

Make sure that “Add Python 3.7 to PATH” which is at bottom is checked and

click on “Install Now” to start the installation.

Then windows operating system shows a pop-up window to ask admin

permission to install the Python. Then click on Yes.

After clicking on Yes, windows start the installation of Python. The

installation screen seems like follows.

After completing installation Windows operating system displays the

following, saying that installation was successful. It seems like the

following screen. Then click on ‘Close’ to complete the installation

process.

PYTHON PROGRAM DEVELOPMENT CYCLE

No compile or link steps

Python programs simply import

modules at runtime and use the

objects they contain.

Because of this, Python programs

run immediately after changes

are made.

Behind the Scenes: How Python Works

INPUT PROCESSING OUTPUT

Most useful programs accept inputs from some source,

process these inputs, and then finally output results to

some destination.

In terminal-based interactive programs, the input source

is the keyboard, and the output destination is the

terminal display.

The Python shell itself is such a program; its inputs are

Python expressions or statements. Its processing

evaluates these items. Its outputs are the results

displayed in the shell.

Python Programming

SYED JANI BASHA

Contents

• Keywords

• Displaying Output with the Print

Function

• Comments

• Variables

• Reading Input from the Keyboard

Python Keywords

Displaying Output with the Print Function

The simplest way to produce output is using the print()

function where you can pass zero or more expressions

separated by commas. This function converts the

expressions you pass into a string before writing to the

screen.

Ex-1: Print(“Hello world”)

Output:

>>>>Hello world

Cont………

Ex-2:

x=5 Print(“X=“,x)

Output:

X=5

Ex-3: print(‘datacamp’, ‘tutorial’ , ‘Python’)

Output:

datacamp

Tutorial

Python

Since the python print() function by default ends with newline.

Python has a predefined format if you use print(a_variable) then it

will go to next line automatically.

Cont…….. sep=’separator’ : (Optional) Specify how to

separate the objects, if there is more than

one.Default :’ ‘

Ex-4: Print(192,168,2,10,sep=“ . ”)

Output:

192.168.2.10

In this example the separator used as dot

operator

Output Formatting

There are several ways to present the output of a program,

data can be printed in a human-readable form, or written

to a file for future use. Sometimes user often wants more

control the formatting of output than simply printing

space-separated values

• Formatting output using String modulo operator(%) :

Ex-1:

# print integer and float value

print("Geeks : % 2d, Portal : % 5.2f" %(1, 05.333))

Output:

Geeks : 1, Portal : 5.33

# print integer value

print("Total students : % 3d, Boys : % 2d" %(240, 120))

# print octal value

print("% 7.3o"% (25))

# print exponential value

print("% 10.3E"% (356.08977))

Output:

Total students : 240, Boys : 12

031

3.561E+0

The first placeholder “%2d” is used for the first component of our tuple, i.e. the integer

1. The number will be printed with 2 characters. As 1 consists only of one digits, the

output is padded with 1 leading blanks.

The second one “%5.2f” is a format description for a float

number. Like other placeholders, it is introduced with the %

character. This is followed by the total number of digits the

string should contain.

This number includes the decimal point and all the digits, i.e.

before and after the decimal point.

Our float number 05.333 has to be formatted with 5

characters. The decimal part of the number or the precision is

set to 2, i.e. the number following the “.” in our placeholder.

Finally, the last character “f” of our placeholder stands for “float”.

• Formatting output using format method User use {} to mark where a variable will be substituted and can

provide detailed formatting directives, but user also needs to provide

the information to be formatted

Ex-1:

# using format() method print('I love {} for its "{}!"'.format(‘india', ‘diversity’))

Output:

I love india for its diversity!

Ex-2:

# using format() method and refering

# a position of the object

print('{0} and {1}'.format(‘India', ‘Diversity')) print('{1} and {0}'.format (‘India', ‘Diversity'))

Output:

India Diversity

Diversity India

Comments

Comments are the useful information that the developers

provide to make the reader understand the source code.

Single line comments :

1.Python single line comment starts with hashtag symbol

with no white spaces (#) and lasts till the end of the line.

2. If the comment exceeds one line then put a hashtag on

the next line and continue the comment.

Ex-:

#program to add two numbers

a, b = 1, 3 # Declaring two integers

sum = a + b # adding two integers

print(sum) # displaying the output

Multi-line string as comment :

Python multi-line comment is a piece of text enclosed in a

delimiter (""") on each end of the comment. Again there

should be no white space between delimiter (""").

Ex-:

"""

This would be a multiline comment in Python that

spans several lines and describes importance of Python in

Computer Science field … """ print(“Python programming")

Python Variables

A variable is a named memory where a programmer can store

data and retrieve for future use using the same name. In Python,

variables are created without specifying any data type.

Syntax

variable_name = value

Example:

roll_number = 101

print(f 'Student roll number is {roll_number}’)

Output:

Student roll number is 101

Declaring multiple variables in a single statement:

In Python, it is possible to define more than one variable using a single

statement. When multiple variables are created using a single statement,

the variables and their corresponding value must be separated with a

comma symbol

Example:

name, roll_number = ('Rama', 101)

print(f 'Student {name} roll number is {roll_number}’)

Output:

Student Rama roll number is 101

Displaying data type of a variable

The Python programming language provides a built-in function

type( ) to display the data type of a variable.

Example:

a = 105

print(type(a))

a = 10.66

print(type(a))

a = 'rama'

print(type(a))

Reading input from keyboard

Python provides us with two inbuilt functions to read the input from the

keyboard.

•input ( prompt )

•raw_input ( prompt ) It is used in older versions of python

input ( ) : This function first takes the input from the user and then evaluates

the expression, which means Python automatically identifies whether user

entered a string or a number or list

Example:

val = input("Enter your value: ")

print(val)

Output:

Enter your value:123

123

Taking multiple inputs from user in Python

In C++/C user can take multiple inputs in one line using scanf but in

Python user can take multiple value Using split() method

Syntax :

input().split(separator, maxsplit)

Example :

x, y = input("Enter a two value: ").split()

print("Number of boys: ", x)

print("Number of girls: ", y)

print()

# taking three inputs at a time

x, y, z = input("Enter a three value: ").split()

print("Total number of students: ", x)

print("Number of boys is : ", y)

print("Number of girls is : ", z)

print()

Python Programming

SYED JANI BASHA

Contents

Operators

Arithmetic Operators

Relational Operators

Assignment Operators

Logical Operators

Identity Operators

Membership Operators

Any All

Type conversions

Expressions

Operators

An operator is a symbol used to perform arithmetical and

logical operations. In other words, an operator can be defined

as a symbol used to manipulate the value of an operand. Here,

an operand is a value or variable on which the operator

performs its task. For example, '+' is a symbol used to perform

mathematical addition operation.

Types of Operators in Python

In Python, there is a rich set of operators, and they are

classified as follows.

• Arithmetic Operators ( +, -, *, /, %, **, // )

• Relational Operators ( <, <=, >, >=, ==, != )

• Assignment Operators ( =, +=, -=, *=, /=, %=, **=, //= )

• Logical Operators ( and, or, not )

• Identity Operators ( is, is not )

• Membership Operators ( in, not in )

• Bitwise Operators ( &, |, ^, ~, <<, >> )

Arithmetic Operators in Python

Examples :

Relational Operators in Python

Examples :

Assignment Operators in Python

Logical Operators in Python

Identity Operators in Python

is and is not are the identity operators both are used to check if

two values are located on the same part of the memory. Two

variables that are equal does not imply that they are identical.

is True if the operands are identical

is not True if the operands are not identical

Membership Operators in Python

Membership operators are used to test whether a value is

present in a sequence. Here the sequence may be String, List,

or Tuple.

Any All in Python

Any and All are two built ins provided in python used for

successive And/Or.

Any

Returns true if any of the items is True. It returns False if empty

or all are false. Any can be thought of as a sequence of OR

operations on the provided iterables.

All

Returns true if all of the items are True (or if the iterable is

empty). All can be thought of as a sequence of AND operations

on the provided iterables.

ANY ALL

Type Conversion or Casting

The process of converting a value from one data type to

another data type is called Typecasting or simply Casting.

Output

Output

Output

Expressions in python

Expressions in python is a statement that include

operators , operands, variables

a = 2

b = 3

d=20

c = a + b*d

print c

e = a * b + d-(a*b)

print d

Python Programming

Syed Jani Basha

Contents

Data Types

None

Numeric data Types

Sequence Types

Mapping Types

Set Types

Python Strings

Using Functions and Modules

Text Type: str

Numeric Types: int, float, complex

Sequence Types: list, tuple, range

Mapping Type: dict

Set Types: set, frozenset

Boolean Type: Bool

None Data Type None

Built-in Data Types

In programming, data type is an important concept.

Variables can store data of different types, and different types can do different

things.

Python has the following data types built-in by default, in these categories:

‘None' data type in Python

In many programming languages, we use the value null to represent

nothing. 'None' is Python's equivalent of NULL value in other

programming languages. In Python, 'None' is the object which represents

nothing. When we want a value to hold nothing, we do assign it with value

'None'.

Example - Python code to illustrate 'None' data type

roll_number = None

print(type(roll_number))

Output: <class ‘NoneType’>

'Numeric' data type in Python

The Python programming language provides four numeric data

types. They are as follows.

•int - All the numbers without fraction part (Example - 10). For

int, there is no upper limit.

•float - All the numbers with a fraction part (Example - 10.5). It’s accurate up to 15 decimal places

•complex - All the numbers with real and imaginary parts

(Example - 5 + 10j).

•bool - boolean values True and False.

Example - Python code to illustrate 'Numeric' data type

a = 10

print(f"the value {a} is of type {type(a)}")

a = 10.5

print(f"the value {a} is of type {type(a)}")

a = 100 + 5j

print(f"the value {a} is of type {type(a)}")

a = False

print(f"the value {a} is of type {type(a)}")

Output:

the value 10 is of type <class 'int'>

the value 10.5 is of type <class 'float'>

the value (100+5j) is of type <class 'complex'>

the value False is of type <class 'bool'>

Sequence Data Types:

A Sequence is an ordered collection of items, indexed by positive

integers. It is a combination of mutable (a mutable variable is one, whose

value can be changed) and immutable (an immutable variable is one, whose

value can not be changed) data types. There are three types of sequence data

type available in Python, they are:

•Strings

•Lists

•Tuples

Strings in Python

A string is a sequence of characters. It can be declared in python

by using double quotes. Strings are immutable, i.e., they cannot

be changed.

Example:

# Assigning string to a variable

a = "This is a string"

print a

Example:

wish_1 = 'Good Morning' wish_2 = "Good Evening“

Output:

Print(wish_1)

Print(wish_2)

Accessing String Values

In Python, whenever a string data value has assigned to a variable, it is

organized as an array of characters. The Python provides a variety of

ways to access the string values. Let's consider the following string value.

Accessing a character from a String Values

wish = 'Good Morning'

print(wish[0])

Output:

G

Example:

wish = 'Good Morning'

print(wish[-2])

o/p:

n

Example:

wish = 'Good Morning'

print(wish[2:8]) # Accessing specified substring

print(wish[:8]) # Here default starting index is '0'

print(wish[2:]) # Here default Ending index is 'Last - (11)’

o/p:

od Mor

Good Mor

od Morning

Lists

It is also a sequence of values of any type. Values in the list are called

elements/items.

Lists are mutable and indexed/ordered. The list is enclosed in square

brackets [ ].

For example, [2, 6, 8, 3, 1] or ["Python", "Java", "C++"] are both lists.

A List is just a bunch of numbers or strings that are kept together inside the

square bracket, sequentially. Each element of the list can be accessed by using

it's index number.

Creating a list in Python

The general syntax for creating a list is as follows.

Syntax

list_name = [element_1, element_2, element_3, ...]

Example:

student_data = [1, 'Rama', '2nd Year', 'CSE', 85.80]

print(student_data)

O/P:

1, 'Rama', '2nd Year', 'CSE', 85.80

Adding Elements to a List:

Using append():Only one element at a time can be added to the list by using append()

method, for addition of multiple elements with the append() method, loops are used.

Using insert():append() method only works for addition of elements at the end of the

List, for addition of element at the desired position, insert() method is used. insert()

method requires two arguments(position, value).

Using extend(): this method is used to add multiple elements at the same time at the end

of the list.

Example: using append()

# Creating a List

List = [ ]

print("Initial blank List: ")

print(List)

# Addition of Elements

# in the List

List.append(1)

List.append(2)

List.append(4)

print("\nList after Addition of Three

elements: ")

print(List)

Output:

Initial blank List:

[ ]

List after Addition of Three

elements:

[1, 2, 4]

Example: using insert()

# Creating a List

List = [1,2,3,4]

print("Initial List: ")

print(List)

# Addition of Element at

# specific Position

# (using Insert Method)

List.insert(3, 12)

List.insert(0, ‘Hello') print("\nList after performing Insert Operation: ")

print(List)

Output:

Initial List:

[1, 2, 3, 4]

List after performing

Insert Operation:

['Hello', 1, 2, 3, 12,4]

Example: using extend()

# Creating a List

List = [1,2,3,4]

print("Initial List: ")

print(List)

# Addition of multiple elements

# to the List at the end

# (using Extend Method)

List.extend([8, 'Geeks', 'Always'])

print("\nList after performing Extend Operation: ")

print(List)

Output:

Initial List:

[1, 2, 3, 4]

List after performing Extend

Operation:

[1, 2, 3, 4, 8, 'Geeks', 'Always']

Accessing elements from the List

# Creating a List with

# the use of multiple values List = [“TeamA", "For", “TeamB"]

# accessing a element from the

# list using index number

print("Accessing a element from the list")

print(List[0])

print(List[2])

# Creating a Multi-Dimensional List

# (By Nesting a list inside a List) List = [[‘TeamA', 'For'] , [‘TeamB']]

# accessing an element from the

# Multi-Dimensional List using

# index number

print("Acessing a element from a Multi-Dimensional list")

print(List[0][1])

print(List[1][0])

Output:

Accessing a element from the list

TeamA

TeamB

Acessing a element from a Multi-Dimensional list

For

TeamB

Negative indexing

List = [1, 2, 'Geeks', 4, 'For', 6, 'Geeks']

# accessing a element using

# negative indexing

print("Accessing element using negative indexing")

# print the last element of list

print(List[-1])

# print the third last element of list

print(List[-3])

Output:

Accessing element using negative indexing

Geeks

For

Removing Elements from the List

Elements can be removed from the List by using built-in remove() function but an Error arises if element doesn’t exist in the set. # Creating a List

List = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

print("Intial List: ")

print(List)

# Removing elements from List

# using Remove() method

List.remove(5)

List.remove(6)

print("\nList after Removal of two elements: ")

print(List)

Output:

Intial List:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

List after Removal of two elements:

[1, 2, 3, 4, 7, 8, 9, 10, 11, 12]

Tuples

A tuple is a collection which is ordered and unchangeable(immutable).

In Python tuples are written with round brackets.

#Create a Tuple:

thistuple = ("apple", "banana", "cherry")

print(thistuple)

#Accessing elements from tuples

thistuple = ("apple", "banana", "cherry")

print(thistuple[1])

#negative indexing

thistuple = ("apple", "banana", "cherry")

print(thistuple[-1])

#Range of indexes

thistuple = ("apple", "banana", "cherry", "orange", "kiwi", "melon", "mango")

print(thistuple[2:5])

#Once a tuple is created, you cannot add items to it. Tuples are

unchangeable.

thistuple = ("apple", "banana", "cherry")

thistuple[3] = "orange" # This will raise an error

print(thistuple)

Output:

('apple', 'banana', 'cherry')

banana

cherry

('cherry', 'orange', 'kiwi')

Tuples are unchangeable, so you cannot remove items from it, but you can delete the

tuple completely:

The del keyword can delete the tuple completely:

thistuple = ("apple", "banana", "cherry")

del thistuple

Join Two Tuples

To join two or more tuples you can use the + operator:

tuple1 = ("a", "b" , "c")

tuple2 = (1, 2, 3)

tuple3 = tuple1 + tuple2

print(tuple3)

Output:

('a', 'b', 'c', 1, 2, 3)

Sets:

A set is a collection which is unordered and unindexed. In Python sets

are written with curly brackets.

#Create a Set:

thisset = {"apple", "banana", "cherry"}

print(thisset)

Output:

{'apple', 'cherry', 'banana'}

Access Items from sets

You cannot access items in a set by referring to an index, since sets are unordered

the items has no index.

But you can loop through the set items using a for loop, or ask if a specified value

is present in a set, by using the in keyword.

Example:

thisset = {"apple", "banana", "cherry"}

for x in thisset:

print(x)

Output:

apple

cherry

banana

Once a set is created, you cannot change its items, but you can add new items.

Add Items

• To add one item to a set use the add() method.

• To add more than one item to a set use the update() method.

Example

#Add an item to a set, using the add() method:

thisset = {"apple", "banana", "cherry"}

thisset.add("orange")

print(thisset)

Output:

{'orange', 'apple', 'cherry', 'banana'}

Example:

Add multiple items to a set, using the update() method:

thisset = {"apple", "banana", "cherry"}

thisset.update(["orange", "mango", "grapes"])

print(thisset)

Output:

{'mango', 'cherry', 'banana', 'apple', 'grapes', 'orange'}

Remove Item To remove an item in a set, use the

remove(), or the discard() method.

Example:

Remove "banana" by using the

remove() method:

thisset = {"apple", "banana", "cherry"}

thisset.remove("banana")

print(thisset)

Output: {'apple', 'cherry’}

remove() raise an error if the item

does not exist

Remove "banana" by using the discard()

method:

thisset = {"apple", "banana", "cherry"}

thisset.discard("banana")

print(thisset)

x = thisset.pop() # It removes the last item

Print(x)

Print(thisset)

Output: {'apple', 'cherry’} {‘cherry’} {‘apple’}

If the item to remove does not exist, discard()

will NOT raise an error.

Join Two Sets

We can use the union() method that returns a new set containing all items

from both sets.

Example:

set1 = {"a", "b" , "c"}

set2 = {1, 2, 3}

set3 = set1.union(set2)

print(set3)

Output:

{'c', 1, 2, 3, 'b', 'a'}

Python Functions A function is a block of code which only runs when it is called.

You can pass data, known as parameters, into a function.

A function can return data as a result.

Creating a Function

In Python a function is defined using the def keyword:

def my_function():

print("Hello from a function")

Calling a Function

To call a function, use the function name followed by

parenthesis:

Example:

def my_function():

print("Hello from a function")

my_function()

Arguments

Information can be passed into functions as arguments.

Arguments are specified after the function name, inside the parentheses. You

can add as many arguments as you want, just separate them with a comma.

The following example has a function with one argument (fname). When the

function is called, we pass along a first name, which is used inside the function

to print the full name:

Example:

def my_function(fname):

print(fname + " Thereja")

my_function(“Reema")

my_function(“Tony")

my_function(“Kevin")

Output:

Reema Thereja

Tony Thereja

Kevin Thereja

Number of Arguments By default, a function must be called with the correct number of arguments.

Meaning that if your function expects 2 arguments, you have to call the

function with 2 arguments, not more, and not less.

Example

This function expects 2 arguments, and gets 2 arguments:

def my_function(fname, lname):

print(fname + " " + lname)

my_function(“Kevin", “Thereja")

Output:

Kevin Thereja

If you try to call the function with 1 or 3 arguments, you will get an error:

This function expects 2 arguments, but gets only 1:

Example

def my_function(fname, lname):

print(fname + " " + lname)

my_function(“Kevin")

TypeError: my_function() missing 1 required positional

argument: 'lname'

Arbitrary Arguments, *args If you do not know how many arguments that will be passed into your function, add a * before the

parameter name in the function definition.

This way the function will receive a tuple of arguments, and can access the items accordingly:

Example:

If the number of arguments is unknown, add a * before the parameter name:

def my_function(*kids):

print("The youngest child is " + kids[2])

my_function(“Tony", "Tiffany", "Linus")

Output:

The youngest child is Linus

Keyword Arguments You can also send arguments with the key = value syntax.

This way the order of the arguments does not matter.

Example

def my_function(child3, child2, child1):

print("The youngest child is " + child3)

my_function(child1 = “Tony", child2 = "Tiffany", child3 = "Linus")

Output:

The youngest child is Linus

The phrase Keyword Arguments are often shortened to kwargs in Python

documentations.

Arbitrary Keyword Arguments, **kwargs

If you do not know how many keyword arguments that will be passed into your function,

add two asterisk: ** before the parameter name in the function definition.

This way the function will receive a dictionary of arguments, and can access the items

accordingly:

Example:

If the number of keyword arguments is unknown, add a double ** before

the parameter name:

def my_function(**kid):

print("His last name is " + kid["lname"])

my_function(fname = “Tony", lname = "Refenes")

Output:

His last name is Refenes

Default Parameter Value The following example shows how to use a default parameter value.

If we call the function without argument, it uses the default value:

Example:

def my_function(country = "Norway"):

print("I am from " + country)

my_function("Sweden")

my_function("India")

my_function()

my_function("Brazil")

Output:

I am from Sweden

I am from India

I am from Norway

I am from Brazil

Passing a List as an Argument

You can send any data types of argument to a function (string, number, list,

dictionary etc.), and it will be treated as the same data type inside the

function.

Example

def my_function(food):

for x in food:

print(x)

fruits = ["apple", "banana", "cherry"]

my_function(fruits)

Output:

apple

banana

cherry

The pass Statement function definitions cannot be empty, but if you for

some reason have a function definition with no

content, put in the pass statement to avoid getting

an error.

Example

def myfunction():

pass

Return Values To let a function return a value, use the return

statement:

Example

def my_function(x):

return 5 * x

print(my_function(3))

print(my_function(5))

print(my_function(9))

Output:

15

25

45

Recursion

Python also accepts function recursion, which means a defined function

can call itself.

Example:

Recursion Example

def tri_recursion(k):

if(k > 0):

result = k + tri_recursion(k - 1)

print(result)

else:

result = 0

return result

print("\n\nRecursion Example Results")

tri_recursion(6)

Output:

21

Python Modules

A module to be the same as a code library.

A file containing a set of functions you want to include in your application.

Create a Module:

To create a module just save the code you want in a file with the file extension .py:

Example:

Save this code in a file named mymodule.py

def greeting(name):

print("Hello, " + name)

Use a Module

Now we can use the module we just created, by using the import

statement:

Example

Import the module named mymodule, and call the greeting function:

import mymodule

mymodule.greeting("Jonathan")

Output:

Hello Jonathan

Variables in Module

The module can contain functions, as already described, but also

variables of all types (arrays, dictionaries, objects etc):

Example

#Save this code in the file mymodule.py

person1 = {

"name": "John",

"age": 36,

"country": "Norway"

}

#Import the module named mymodule, and access the person1 dictionary:

import mymodule

a = mymodule.person1["age"]

print(a)

Output:36

Re-naming a Module

You can create an alias when you import a module, by using

the as keyword:

Create an alias for mymodule called mx:

import mymodule as mx

a = mx.person1["age"]

print(a)

Output:36

Import From Module

You can choose to import only parts from a module, by using the from

keyword.

Example

#The module named mymodule has one function and one dictionary:

def greeting(name):

print("Hello, " + name)

person1 = {

"name": "John",

"age": 36,

"country": "Norway"

}

#Import only the person1 dictionary from the module:

from mymodule import person1

print (person1["age"])

Output:36

Python Programming

Syed Jani Basha

Contents

Decision Structures

if

if-else

if-elif-else

Nested Decision structures

More on Strings methods

Python Conditions and If statements

Python supports the usual logical conditions from mathematics:

Equals: a == b

Not Equals: a != b

Less than: a < b

Less than or equal to: a <= b

Greater than: a > b

Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly

in "if statements" and loops.

In python different decision statements are

If

If-else

If-elif-else

Nested if

If statement An "if statement" is written by using the if keyword.

Example

If statement:

a = 33

b = 200

if b > a:

print("b is greater than a")

Indentation

Python relies on indentation (whitespace at the

beginning of a line) to define scope in the code. Other

programming languages often use curly-brackets for

this purpose.

If statement, without indentation (will raise an error):

a = 33

b = 200

if b > a:

print("b is greater than a") # you will get an error

Using if-else

a = 200

b = 33

if b > a:

print("b is greater than a")

else:

print("b is not greater than a")

Elif

The elif keyword is pythons way of saying "if the previous

conditions were not true, then try this condition".

Example

a = 33

b = 33

if b > a:

print("b is greater than a")

elif a == b:

print("a and b are equal")

If-elif-else

a = 200

b = 33

if b > a:

print("b is greater than a")

elif a == b:

print("a and b are equal")

else:

print("a is greater than b")

a is greater than b, so the first condition is not true, also the elif

condition is not true, so we go to the else condition and print to screen

that "a is greater than b".

Short Hand If If you have only one statement to execute, you can put it on the same line as the if statement.

Example

One line if statement:

if a > b: print("a is greater than b")

Short Hand If ... Else If you have only one statement to execute, one for if, and one for else, you can put it all on the same

line:

Example

One line if else statement:

a = 2

b = 330

print("A") if a > b else print("B")

This technique is known as Ternary

Operators, or Conditional Expressions.

Nested If

You can have if statements inside if

statements, this is called nested if statements.

Example

x = 41

if x > 10:

print("Above ten,")

if x > 20:

print("and also above 20!")

else:

print("but not above 20.")

The pass Statement

if statements cannot be empty, but if you for some

reason have an if statement with no content, put in the

pass statement to avoid getting an error.

Example

a = 33

b = 200

if b > a:

pass

String Methods

The strip() method removes any whitespace from the

beginning or the end:

a = " Hello, World! "

print(a.strip()) # returns "Hello, World!"

The lower() method returns the string in lower case:

a = "Hello, World!"

print(a.lower())

The upper() method returns the string in upper case:

a = "Hello, World!"

print(a.upper())

Hello, World!

hello, world!

HELLO, WORLD!

The replace() method replaces a string with

another string:

a = "Hello, World!"

print(a.replace("H", "J"))

Jello, World!

The split() method splits the string into substrings

if it finds instances of the separator:

a = "Hello, World!"

print(a.split(",")) # returns ['Hello', ' World!']

['Hello', ' World!']

String Concatenation

Merge variable a with variable b into variable c:

a = "Hello"

b = "World"

c = a + b

print(c)

HelloWorld

String Format

age = 36

txt = "My name is John, I am " + age

print(txt)

But we can combine strings and numbers by using the format() method!

The format() method takes the passed arguments, formats them, and places them

in the string where the placeholders {} are:

Use the format() method to insert numbers into strings:

age = 36

txt = "My name is John, and I am {}"

print(txt.format(age))

quantity = 3

itemno = 567

price = 49.95

myorder = "I want {} pieces of item {} for {} dollars."

print(myorder.format(quantity, itemno, price))

Python Programming

Syed Jani Basha

Contents

Repetition Structures

while loop

for loop

Calculating running total

Input validation loops

Nested loops

While Loops

With the while loop we can execute a set of statements as long as

a condition is true.

Example

#Print i as long as i is less than 6:

i = 1

while i < 6:

print(i)

i += 1

Output:

1

2

3

4

5

Note:increment i value otherwise

loop continues for ever

Using break

Exit the loop when i is 3:

i = 1

while i < 6:

print(i)

if i == 3:

break

i += 1

Output:

1

2

3

Using else with while

#Print a message once the condition is false:

i = 1

while i < 6:

print(i)

i += 1

else:

print("i is no longer less than 6")

Output:

1

2

3

4

5

i is no longer less than 6

Python For Loops

A for loop is used for iterating over a sequence (that is either a list, a tuple, a

dictionary, a set, or a string).

This is less like the for keyword in other programming languages, and works

more like an iterator method as found in other object-orientated programming

languages.

With the for loop we can execute a set of statements, once for each item in a list,

tuple, set etc.

Example:

fruits = ["apple", "banana", "cherry"]

for x in fruits:

print(x)

The range() Function

To loop through a set of code a specified number of times, we can use the

range() function,

The range() function returns a sequence of numbers, starting from 0 by

default, and increments by 1 (by default), and ends at a specified

number.

Using the range() function:

for x in range(6):

print(x)

0

1

2

3

4

5

for x in range(2, 6):

print(x)

Output:

2

3

4

5

#Increment the sequence with 3 (default is 1):

for x in range(2, 30, 3):

print(x)

output

2

5

8

11

14

17

20

23

26

29

Nested Loops

A nested loop is a loop inside a loop.

The "inner loop" will be executed one time for each iteration of the

"outer loop": Print each adjective for every fruit:

adj = ["red", "big", "tasty"]

fruits = ["apple", "banana", "cherry"]

for x in adj:

for y in fruits:

print(x, y)

Output:

red apple

red banana

red cherry

big apple

big banana

big cherry

tasty apple

tasty banana

tasty cherry

Calculating running totals

total=0 #accumulator

another_number_to_add=True

while another_number_to_add == True:

number=int(input('Enter a number:'))

total=total+number

answer=input('Want to add another

number?')

if answer == 'Y':

another_number_to_add=True

else:

another_number_to_add=False

print('Here is u r total:',total)

Output:

Enter a number:5

Want to add another number?Y

Enter a number:6

Want to add another number?Y

Enter a number:9

Want to add another number?N

Here is u r total: 20

#Another way

total=0

for number in [8,6,7,5,]:

total=total+number

print('Here is the total:',total)

Output:

26

Precise way

total=0

number_of_numbers=int(input('How many?')

for n in range(number_of_numbers):

number=int(input('Give the next number:'))

total=total+number

print('Here is Your total:',total)

How many?5

Give the next number:6

Give the next number:9

Give the next number:5

Give the next number:4

Give the next number:1

Here is Your total: 25

Validating Inputs:

When we accept user input we need to check that it is valid. This checks to

see that it is the sort of data we were expecting. There are two different wa

ys we can check whether data is valid.

Method 1: Use a flag variable. This will initially be set to False. If we

establish that we have the correct input then we set the flag to True. We

can now use the flag to determine what we do next (for instance, we might

repeat some code, or use the flag in an if statement).

Method 2: Use try/except. Here, we try to run a section of code. If it doesn’t work (for instance, we try to convert a string to a number, but it doesn’t contain a number) then we run the except block of code.

Types of validation:

Validation technique Meaning

Type check Checking the data type e.g. int, float etc.

Length check Checking the length of a string

Range check Checking if a number entered is between two numbers

while True:

try:

age = int(input('How old are you? '))

break

except ValueError:

print('Please enter a whole number')

print('Your age is: ' + str(age))

Example - A length check using a flag

isLongEnough = False

while not isLongEnough:

password = input('Enter password at least 5 characters: ')

if len(password) >= 5:

isLongEnough = True

else:

print('Password entered is too short')

print('Your password entered is: ' + password)

Example - A range and type check using a flag and exception

isTeenager = False

while not isTeenager:

try:

age = int(input('How old are you? '))

if age >= 13 and age <= 19:

isTeenager = True

except:

print('You must enter a valid number between 13 and 19')

print('You are a teenager aged ' + str(age))

Thank you