Mr Nuwan Kodagoda

Head/Department of Information Technology

Sri Lanka Institute of Information Technology

GCE (A/L) ICT Training for Teachers (Last Updated on 21st March 2011)

Outcomes

Introduction to Python
Data Types and Calculations
Selection
Repetition
String Handling
Functions
Lists
File Handling
Classes

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Programming Languages

Programming Languages

There are hundreds of programming

languages.
Very broadly these languages are
categorized as
o
o

Low Level Languages

High Level Languages

Low Level Languages

More closer to the Architecture of the

computer.
Very difficult for us humans to use.
Machine Code
Memory
Addresses

Assembly

High Level Languages

High Level Languages are closer to

human languages.
Dim radius as integer
Dim area as integer
radius = txtRadius.text
area = 22/7*radius*radius
msgbox area

How a Computer Program works

The Program you write is executed by

the CPU.
Since the CPU can only understand
machine code your program needs to
be converted into machine code.

How a Computer Program works

Dim radius as integer

Dim area as integer
radius = txtRadius.text
area = 22/7*radius*radius
msgbox area

Source
Code

C8
B7
23A7
D7
AA
89
DD
89D23
A9
F4
A9
...

Machine Code

How a Computer Program works

The software that does the conversion

to machine code comes in two flavours.
Compilers
Interpreters

What is a Compiler?

A compiler converts your entire

program to machine code at one go.
After compilation you have an
executable file.
e.g. an EXE, COM file for PCs

How an Interpreter Works

An Interpreter converts your program to

machine code one instruction at a time.

Python

Python is an easy to learn, powerful

programming language.
It has efficient high-level data structures
and a simple but effective approach to
object-oriented programming.
Python is an ideal language for
scripting and rapid application
development in many areas on most
platforms.
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Python Language

No variable, data type declaration

necessary (Dynamically Typed)
Case Sensitive variables
Indentation of 4 characters used for
block structures (e.g. if, while,
functions)
Program extension is .py
Runs on multiple platforms
Open Source
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Python Keywords

Like most modern languages Python

has only a few keywords.

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History

Developed in the early

1990s by Guido van
Rossum.
The name Python was
based a popular TV show
called the Monty Python.

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Which version of Python should I use?

There are two versions of Python

available
Python 2 the latest is 2.71
Python 3 the latest is 3.2
For the ICT exam use Python 2
Some differences e.g. in Python 3 the
print is a function so print 10, 20 has to
be written as print(10,20)

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Downloading Python and Installing

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Operator Precedence

Operator

Description

Associatively

* / %

Multiplication/division/modulus

left-to-right

+ -

Addition/subtraction

left-to-right

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Arithmetic Operators

(Python 3 only)

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MCQ Question 41

r=11; y=2.5; c=4 have been assigned to

three variables
Find the value of r%3*c+10/y

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MCQ Question 41

r=11; y=2.5; c=4 have been assigned to

three variables
Find the value of r%3*c+10/y
11%3*4+10/2.5
2*4+10/2.5
8+10/2.5
8+4.0
12.0

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Numerical Calculations

10+20/2
(10+20)/2

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Printing values in Python

print 10, Nadun, 1990

In Python 3 print is a function
print(10, Nadun, 1990)

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Input Data in Python 2

no1 = int(input(Enter an int Number : ))

no2 = float(input(Enter a float Number : ))
str = raw_input(Enter a string : )

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Calculations

Write a python program to input a

length in mm and convert it to inches.
25.4 mm = 1 inch

inches.py

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Calculations

Write a python program to input a

temperature in Celcius and convert it to
Fahrenheit.
fahrenheit = 9/5* celcius +32

celcius.py

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Selection

if (cond) then
Statement A

else
Statement B

endif

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Selection

if (cond) then
Statement A

else
Statement B

endif

if cond:
Statement A

else:
Statement B

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if statement

Write a program to input a mark and

display Pass if it is greater than or
equal to 50. Otherwise display Fail.

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if statement

Write a program to input a number.

Display if it is an even or an odd
number.
oddeven.py

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Nested if statement

if (test1) then
block1
else if (test2) then
block2
else
elseBlock
endif
endif

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Nested if statement

if (test1) then
block1
else if (test2) then
block2
else
elseBlock
endif
endif

if test1:
block1
elif test2:
block2
else:
elseBlock

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Nested If Statement

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Grades

Write a program to input the marks of a

student and calculate the grades.
> 75 A
65 to 75 B
55 to 64 C
45 to 54 S
< 45 - W

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Nested If Statement

Write a program to input an amount and

to calculate the discount as follows.
Discounts
>1000 - discount 10%
500-1000 - discount 5%
< 500 - discount 2%

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MCQ Question 42

What would be the output of this

program.

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MCQ Question 42

If 10<4 or 10!=4
false or true
true

j = j-y
j = 10-4
j=6
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Repetition

do while (cond)
execute Statement

end while

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Repetition

do while (cond)
execute Statement

end while
while cond:
execute Statement

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while

Write a program to Print numbers 1 to 9

while1.py

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while

Write a program to Print numbers

1,3,5,7,9

while2.py

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while

Write a program to print the tables of 7.

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Using For loop in Python

Range command generates a list.

A list is similar to an array, but it can
store data of different types. It also
could contain another list.
range(1,10) produces the list
[1,2,3,4,5,6,7,8,9]
for r in range(1,10):
print(r)
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Using For loop in Python

range(1,10,2) produces the list

[1,3,5,7,9]

for r in range(1,10,2):
print(r)

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Using For loop in Python

Any list can be printed in the same way

Mylist = [Java,C#, VB6,
VB.NET,Python]
for r in Mylist:
print(r)
Java
C#
VB6
VB.NET
Python

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Using For loop in Python

This works the same for a string

country = SRI LANKA

for r in country:
print(r)

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S
R
I
L
A
N
K
A

MCQ Question 43

What would be the

output ?

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MCQ Question 43

What would be the

output ?
r= 5
s=3
r = r+s
r = 5+3 = 8
s = r+3=8+3
print 11
r<25 = 11<25 false
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MCQ Question 43

What would be the

output ?
r=8
s=11
r = r+s
r = 8+11 = 19
s = r+3=19+3=22
print 22
r<25 = 22<25 false
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MCQ Question 43

What would be the

output ?
r=19
s=22
r = r+s
r = 19+22 = 41
s = r+3=41+3=44
print 44
r<25 = 44<25 false
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MCQ Question 44

Select the correct pseudo

code for the given flow
chart

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MCQ Question 45

Which of the above

statements are correct

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String Manipulation

mystr = Sri Lanka

len(mystr)
mystr.upper() # upper case
mystr.upper() # lower case
mystr[0] # S
mystr[-1] # a

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List Manipulation

mylist = [10, Ajith, 67.3, 78.2]

mylist[0] # 10
mylist[3] # 78.2
mylist[-1] # 78.2
mylist[-2] # 67.3
sublist = mylist[1:3] # [Ajith, 67.3]
sublist = mylist[1:] # [Ajith, 67.3, 78.2]

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List Manipulation

len(mylist) #4
mylist.append(89) # adds 89
# [10, Ajith, 67.3, 78.2, 89]
mylist.sort() # sorts list
mylist.reverse() # reverses list

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Break and Continue

A break statement inside a block will

cause it to exit the loop
A continue statement inside a block will
skip the remaining instructions and go
to the beginning of the loop.

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Question II 3

AQ3c.py

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p
y
t
h
o
n

Question II 3

pythonprogramming
(one letter per line)
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AQ3d.py

Part B Question 5

1 Cat 3
2 Dog 3
3 Rat 3

BQ5b.py

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Functions

A function that returns a value or does a

particular task
def cube(x):
return x*x*x
cube(10)

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Functions

Write a function that converts mm to

inches

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Example

Write a python program that returns the

maximum of two numbers
max(10,30) # should return 30

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Importing modules and functions

import pythonprg
pythonprg.func1(3)

from pythonprg import func1,

func2
func1(3)

Assume there is a program called

pythonprg.py which has two functions
named func1() and func2()
To use these functions from another
python program we need to do the
following.
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Setting PYTHONPATH

StartCMD
SET PYTHONPATH=
c:\python27;c:\python27\programs
Importing modules from IDLE
import sys
sys.path.append(c:\\python27\\programs)

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Part B Question 5

BQ5b2.py

5x1=5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50
5 x 11 = 55

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Question II 3

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Pseudo Code for above flow chart

# Pseudo code
#x=1
# total = 0
# do while (x <= 10)
# input marks
# x=x+1
# total = total + marks
# end while
# avg = total/(x-1)
# if (avg>50) then
# display "Good"
# else
# display "Bad"
# endif

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Python Code
x=1
total = 0
while x <= 10:
marks = int(input("Enter marks : "))
total = total + marks
x=x+1
avg = total/(x-1)
print "total ",total
print "avg ", avg
if avg>50:
print "Good"
else:
print "Bad"

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File Handling

Python allows you to easily read and

write data files

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Write data to a file

Write a sample program to store data to

a data file where commas separate
values.
datafile = open ("marks.dat","w")
datafile.write(<str>)

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Read data from a file

Write a sample program to read data

from a data file where commas
separate values.
datafile = open ("marks.dat","r")
record = datafile.readline()
# split the data into a list for easier
manipulation. The comma is the seperator
mylist = record.strip(\n).split(,)

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Part B Question 5

BQ5c.py

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Object Oriented Program

Python Supports OO just like any other

modern programming language
Python code as usual is minimilistic
Both methods and attributes can be
accessed from outside.

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Classes and Objects

A person working
In a company

Person
EmpNo
Name
Address
BasicSal
OtHrs
OtRate
CalcOtAmt
CalcNetSal

Properties

Methods

Classes and Objects

You describe the

objects details in a
Class. A class is a blue
print of an object.
House1

Blue Print

House2
House3

Classes

# Shape.py
class Rectangle:
def __init__(self,x,y):

def display(self):

import Shape
rec1 = Shape.Rectangle(10,20)
rec1.display()
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Classes

# Shape.py
class Rectangle:
def __init__(self,x,y):

def display(self):

from Shape import Rectangle

rec1 = Rectangle(10,20)
rec1.display()
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Circle

Write a class to represent a circle

Calculate the area pi*r^2
Calculate the perimeter 2*pi*r

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MCQ 50

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MCQ 50

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MCQ 49

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Exercises

Write a program to input a series of

numbers terminated by -999. Calculate
and print the sum of the numbers
entered.

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Exercise

Write a program to input the sum of 10

numbers.
Modify the above program using a
break statement so that when the
number -999 is entered it will stop the
entering of marks
Modify the above program to ignore
negative numbers (except for -999).
Use the continue statement
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