This document provides an introduction to computing and programming concepts such as what a computer program is, binary and machine code, assembly code, interpreters and compilers, structured programs using sequences, branches, loops and modules. It discusses programming concepts like variables, strings, arithmetic operations, conditional statements, loops, functions, modules and file input/output. The key points are that a computer program is a set of instructions, programming involves different levels of representation from binary to assembly to high-level languages, and programming uses basic constructs like sequences, branches, loops to structure programs.

1. Computing
and
programming
workshop
Dan Bowen
Carine Jacquel

2. What is a computer program?
A computer program is simply a set of
instructions to tell a computer how to perform a
particular task.
Picture: Charles Babbage – Difference engine

3. Binary - Machine Code
Binary
0110 0001
0110 0010
Machine Code
001273 05 04
001273 06 04

4. Assembly code
To add two numbers the (binary) machine code
could be :
001273 05 04
Assembly code meant that the intial programmers
had an interface for the binary
A typical assembler line could be
ADD 05 04

5. Interpreter and Compiler
A programmer writes a program in a high level
language (Source Code)
This is interpreted into the bytes that the computer
understands (Object code – often called binary
code, machine code)
The interpreter has a couple of names, one being
the interpreter and the other being the compiler.

6. Structured programs
Edsger Dijkstra came up with several key
principles that all structured programs require:
•
•
•
•
Sequences
Branches
Loops
Modules
Top Tip – Get the kids to use
flowcharts before hand. This
is good practice and helps for
program design.

7. Sequences

8. Branching
Q : Can you think
of a situation you
might use a
branch?
Path 1
Step 1
Test
condition
Path 2

9. Loops
Repeated
Steps
Q : Can you think
of a situation you
might use a Loop?
Test
Condition

10. The art of debugging
• Making errors (syntax, runtime, semantic)
• Resolving errors

11. Our first program
>>> print “Hello World”
What happens if you type
>>> Print “Hello World”

12. A quick pocket calculator….
>>> print 5 + 6
Functions + -
* /
Try it… have a go at some more calculations. When doing
maths remember
BIDMAS (Brackets, Indices, Division, Multiplication and
Subtraction)
>>> print ((6 * 5) + (7 - 5)) / (7 + 1)

13. Integers and real numbers
>>> print 5/2
>>> print 5/2.0
Modulo
>>> print 7/2
3
>>> print 7%2
1
What is an
integer?
What is a real
number?

14. Joining strings and numbers
>>>print 'The total is: ', 23+45
Activity : Have a Play
This is called
Concatenation

15. Combining text and numbers
>>> print "The sum of %d and %d is: %d" % (7,18,7+18)
• %s - for string
• %x - for hexadecimal number
• %0.2f - for a real number with a maximum of 2 decimal
places
• %04d - pad the number out to 4 digits with 0's

16. >>>import sys
• Some Python programs will use extra ‘objects’
and ‘functions’
• An example of this is import.sys
An example of this could be
>>>import sys
>>>sys.exit()

17. Variables
>>> q = 7
>>> print q
7
>>> q = "Seven"
>>> print q
Seven
# q is now a number
# reassign q to a string

18. Good practice - A note about
comments
Poor:
v = 3600
s = t*3600
Better:
v = 3600
s = t*3600
# this is an integer set at 3600
# t is time
# 3600 is num of secs in an hour
# t holds elapsed time in hours, so convert to secs

19. Text variables
With single quotes: 'Here is a string'
With double quotes:
"Here is a very similar string"
With triple double quotes:
""" Here is a very long string that can if we wish
span several lines and Python will preserve the lines
as we type them..."""

20. Manipulating strings
• There are several sub functions on each
programming language that allow you to treat
text like and array and do things such as
– find a sub string
– join two strings (concatenation)
– copy one to another

21. >>> print 'Again and ' + 'again'
Again and again
>>> print 'Repeat ' * 3
Repeat Repeat Repeat
>>> print 'Again ' + ('and again ' * 3)
Again and again and again and again
We can also assign character strings to variables:
>>> s1 = 'Again '
>>> s2 = 'and again '
>>> print s1 + (s2 * 3)
Again and again and again and again

22. Integers
Operator Example
Description
M+N
Addition of M and N
M-N
Subtraction of N from M
M*N
Multiplication of M and N
M/N
Division, either integer or floating point
result depending on the types of M and
N. If either M or N are real numbers(see
below) the result will be real.
M%N
Modulo: find the remainder of M divided
by N
M**N
Exponentiation: M to the power N

23. Not sensible maths but vital in
programming
>>> x = 42
>>> print x
>>> x = x + 1
>>> print x
Python also has a shortcut for this
>>> x += 1
>>> print x

24. Boolean Operators
Operator Example
Description
Effect
A and B
AND
True if A,B are both True,
False otherwise.
A or B
OR
True if either or both of A,B
are true. False if both A
and B are false
A == B
Equality
True if A is equal to B
Inequality
True if A is NOT equal to B.
Negation
True if B is not True
A != B
or
A <> B
not B

25. Using IDLE or text editor
# File: firstprogram.py
print "hello world"
print "Here are the ten numbers from 0 to 9n0
1 2 3 4 5 6 7 8 9"
print "I'm done!"
# end of file
Notepad, IDLE or
any text editor can
be used for this….

26. IDLE – All in one solution
Integrated DeveLopment Environment
Allows you to edit and run programs
Activity
Create a NEW program
Run it (F5)

27. FOR loops
>>>for i in range(1,11):
…
print i
# must be indented
What do you think this code does?
>>>for i in range(1,13):
...
print "%d x 12 = %d" % (i, i*12)

28. While loops
(if we don’t know the number of iterations)
>>> j = 1
>>> while j <= 12:
...
print "%d x 12 = %d" % (j, j*12)
...
j=j+1

29. Nested loops
>>> for multiplier in range(2,13):
...
for j in range(1,13):
...
print "%d x %d = %d" % (j,multiplier,j*multiplier)
…
print “------------” # this separates the tables

30. Other loops
• do-while - Same as a while but the test is at the end so the
loop always executes at least once.
• repeat-until - Similar to above but the logic of the test is
reversed.
• GOTO, JUMP, LOOP etc Mainly seen in older languages, these
usually set a marker in the code and then explicitly jump
directly to that marker.

31. Good practice tip – Add some style
#############################
# This is my first program
# Author: Dan Bowen
# Date: 27/02/2013
# Version: Draft 1 ''' This program is a simple starter
# program to help learn python
###############################
# Log: Added a variable to fix the counter 28/02/2013 DB
# File created 27/02/2013
################################
import sys,
Print”Hello World”

32. Talking to the user
>>> resp = raw_input("What's your name? ")
>>> print "Hi, %s, nice to meet you" % resp
Have a play with this

33. The Input() function
multiplier = input("Which multiplier do you want? Pick a number ")
for j in range(1,13):
print "%d x %d = %d" % (j, multiplier, j * multiplier)
Input is clever and tries to evaluate the type of data such as integers
(numbers) which can then be used to calculate things.

34. However….
>>>multiplier = int(raw_input("Which multiplier do you want? Pick a number "))
>>>for j in range(1,13):
...
print "%d x %d = %d" % (j, multiplier, j * multiplier)
Input() can be used to delete files etc….so often it's better to stick to raw_input()
and convert the string into the data type you need using Python's built in
conversion functions.

35. Branching
A classic example. What does this program do?
10 PRINT "Starting at line 10"
20 J = 5
30 IF J < 10 GOTO 50
40 Print “Hello World"
50 STOP

36. If Statements to branch
import sys
# only to let us exit
print "Starting here"
j=5
if j > 10:
print "This is never printed"
else:
sys.exit()

37. Combining Logical elements and IF’s
save time
if value > maximum:
print "Value is out of range!“
else if value < minimum:
print "Value is out of range!"
---------------------------------if (value < minimum) or (value > maximum):
print "Value is out of range!"

38. Chaining IF Statements
if price == 100:
print "I'll take it!"
What does == represent?
What would happen if 200 and 500
else:
were switched?
if price > 500:
print "No way Jose!"
else:
if price > 200:
print "How about throwing in a freemouse ?"
else:
print "price is an unexpected value!"

39. Multi function IF
menu = """
Pick a shape(1-3):
1) Square
2) Rectangle
3) Triangle """
shape = int(raw_input(menu))
if shape == 1:
length = float(raw_input("Length: "))
print "Area of square = ", length ** 2
elif shape == 2:
length = float(raw_input("Length: "))
width = float(raw_input("Width: "))
print "Area of rectangle = ", length * width
elif shape == 3:
length = float(raw_input("Length: "))
width = float(raw_input("Width: "))
print "Area of triangle = ", length * width/2
else:
print "Not a valid shape, try again"

40. A little bit on modules
The idea of programming with modules is to
allow the programmer to extend the built in
capabilities of the language. It packages up bits
of program into modules that we can 'plug in' to
our programs.

41. Some examples
• pow(x,y)
• To find out the variables within a module
>>> import sys
>>> dir(sys)
Have a play with the modules on the following slide

42. Module name
Description
sys
Allows interaction with the Python system: exit() exit! argv - access command line arguments path
- access the system module search path ps1 change the '>>>' python prompt!
Allows interaction with the operating system:
name - the current operating system, useful for
portable programs system - execute a system
command mkdir - create a directory getcwd - find
the current working directory
Allows manipulation of strings with Unix style
regular expressions search - find pattern
anywhere in string match - find at beginning only
findall - find all occurences in a string split - break
into fields separated by pattern sub,subn - string
substitution
Allows access to many mathematical functions:
sin,cos etc - trigonometrical functions log,log10 natural and decimal logarithms ceil,floor - ceiling
and floor pi, e - natural constants
time(and date) functions time - get the current
time (expressed in seconds) gmtime - convert
time in secs to UTC (GMT) localtime - convert to
local time instead mktime - inverse of localtime
sleep - pause program for n seconds
random number generators - useful for games
programming! randint - generate random integer
between inclusive end points sample - generate
random sublist from a bigger list seed - reset the
os
re
math
time
random

43. Files
Assume we have a file called menu.txt This contains
spam & eggs
spam & chips
Spam & spam
Open and reading the file
inp = file("menu.txt","r")
inp.readlines():
print line
inp.close()

44. A simple file copy
# Create the equivalent of: COPY MENU.TXT MENU.BAK
# First open the files to read(r) and write(w)
inp = open("menu.txt","r")
outp = open("menu.bak","w")
# read file, copying each line to new file
for line in inp: outp.write(line)
print "1 file copied..."
# Now close the files
inp.close()
outp.close()

45. Another file example
import time
# Create daily menu based on MENU.TXT
# First open the files to read(r) and write(w)
inp = open("menu.txt","r")
outp = open("menu.prn","w")
# Create todays date string
today = time.localtime(time.time())
theDate = time.strftime("%A %B %d", today)
# Add Banner text and a blank line
outp.write("Menu for %snn" % theDate)
# copy each line of menu.txt to new file
for line in inp: outp.write(line)
print "Menu created for %s..." % theDate
# Now close the files
inp.close()
outp.close()

46. Program design
•
•
•
•
Comments
Variable names
Program names
Block structure – Python important!

47. A word on Object Orientation
Most languages these days are object
orientated. This enables code to be reused and
saves on developmental costs.

48. Object Orientation in Python –
complex classes
Classes are complex user defined ‘objects’
>>>class Address: ... def __init__(self, Hs, St, Town, Zip):
... self.HsNumber = Hs
... self.Street = St .
.. self.Town = Town
... self.ZipCode = Zip
...
>>> Addr = Address(7,"High St","Anytown","123 456")
>>> print Addr.HsNumber, Addr.Street

49. OO using the class
Essentally we import the module, create an
instance of Spam, assigning it the name mySpam
and then use mySpam to access its operations
and data:

50. Points to remember
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
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Programs control the computer
Programming languages allow us to 'speak' to the computer at a level that is closer
to how humans think than how computers 'think'
Error messages are nothing to be scared of, read them carefully, they usually give a
clue as to why you got them.
But it's only a clue... if in doubt check the lines immediately before the reported
line.
Python does math almost the way you'd expect
To get a fractional result you must use a fractional number
You can combine text and numbers using the % format operator
IDLE is a cross platform development tool for writing Python programs.
Comments can make programs clearer to read but have no effect on the operation
of the program
Variables can store intermediate results for later use
FOR loops repeat a set of commands for a fixed number of iterations.
WHILE loops repeat a set of commands until some terminating condition is met.
They may never execute the body of the loop if the terminating condition is false
to start with.
Use if/else to branch
The else is optional
Multiple decisions can be represented using a Case or if/elif construct
Boolean expressions return True or False

51. Thank you