0. Computer Programming Fundamentals
Introduction to Python

1. Agenda Introduction Computer Programs Python Variables Assignment
The Python shell
Variables
Assignment
A first program

2. Computer Programs Computer Programs Programming languages Python
Web browser
Spread sheet
Programming languages
Human-readable
Converted to a form the computer can execute
Compiler
Interpreter
Python
An interpreted language

3. Python shell Python can be used as a command line interpreter
Reads ‘commands’ from the console
Writes results back
Can use this mode to try stuff out

4. “Hello World!”

5. Python shell as a calculator

6. Variables Little bits of the computer’s memory
We assign them an identifier so we can refer to them
When we put stuff into a variable, the computer will remember it for us
Later we can get that stuff back again
We can retrieve the variable’s contents at any time

7. Identifiers and Keywords
Names you can make up
Must begin with a letter or underscore
( _ )
Can then have letters, numbers and underscores
Keywords
Words that have a special meaning
Cannot use them as identifiers
Examples - if , while, for

8. Identifiers aName 23HighSt _special_ A name HighSt23 joe@somewhere
Examples of identifiers:
aName
23HighSt
_special_
A name
HighSt23
while

9. Using variables aVariable = 123 X = aVariable aString = "A string"
anotherString = 'The value of y is '
a = X + 4
y = a
print(anotherString+str(y))
The value of y is 127

10. Variable type Variables have an associated type
This type defines what sort of information the variable contains
Examples of variable type:
Numbers
int, float, complex
Strings of characters
Boolean values
True
False

11. Using the console Writing to the console
print("Message ...")
Reading input from the console
name = input("Enter name:")
name now contains the value entered

12. Writing programs Can store groups of ‘statements’ for execution later
We do not have to type them all in again
Later we will learn how to control the flow through the stored statements
Such a group of statements is a program

13. A first program
##################################### # First program # print("Starting first program!") enteredValue = input("Enter value:") print("Value entered was - ",end="") print(enteredValue)

14. Running our first program

15. Program design
Before embarking on the coding process it is usually a good idea to design your program
Designing your program means
Thinking about how your program is to work
Recording the decisions you have made in order to communicate your design to others
Many possible ways to record your design
Flowcharts
Pseudo-code

16. Flow charts Terminator Input and output Start Start Print message
Finish
Prompt &
Get reply
Confirm
value
Terminator
Input and output
Start
Print
message 16

17. Flow charts print("Starting first program!")
message
Start
Finish
Prompt &
Get reply
Confirm
value
print("Starting first program!")
enteredValue = input("Enter value:")
print("Value entered was - ",end="")
print(enteredValue) 17

18. Exercises Exercise 1 Exercise 2 Exercise 3 Exercise 4
Exploring the command line
Exercise 2
The famous ‘Hello World!’ program
Exercise 3
Using the console
Exercise 4
Dealing with ‘types’