Computer Programming Fundamentals Introduction to Python

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

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

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

“Hello World!”

Python shell as a calculator

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

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

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

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

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

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

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

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

Running our first program

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

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

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

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’