Languages Solve problems using a computer give the computer instructions Remember our diaper changing exercise Talk the talk Speak its language High level Python C Java Low level machine language computers can only execute these High level languages have to be processed into low level before the computer can run them But high level languages can run on different kinds of computers and are easier for humans to write and read so most programs are written in high level Translation How does high level get translated into low level Interpreters and compilers Interpreter processes the program a little bit at a time and runs it Compiler translates everything before running it What is Python is a programming language that lets you work more quickly and integrate your systems more effectively in other words magic http www python org Python Vocab Program A larger file of code that may contain one or more functions Variable names that you can assign values to allowing you to reuse them later on E g x 1 or msg Hi I m a message Comments These are notes ignored by the computer In Python comments start with a hash mark and end at the end of the line E g x y both variables store user input Operators Mathematical symbols like and but also for exponents Python Vocab Keyword Words with meaning purpose in Python E g and print and if Function A chunk of code that performs an action Functions have names and are reusable Kinds built in ones and user defined ones Expression Statements that produce values Examples include 3 5 Hello world Error When your program has a problem the command area will provide an error message What is JES Jython Environment for Students allows you to program and experiment with python The top part the white window with the tiny number 1 which tells you that that s line number 1 or the program area works like any text editor would where you can type stuff and save it under some file name so you can close it and pull it back up later The bottom part in black the command area is the brains of the operation After you are done writing a program here Click Load Program to compile the program Writing Your Program Header Comments file name circ py author Durrah Almansour description a program to calculate the area of a circle Indentation Not an Option but a Requirement In Python indenting specifies the scope of different chunks of your code def main print Hello world The print line will be executed when you invoke main Writing Your Program Always plan what you want your program to do pseudocode Divide it into parts it will make it easier to debug and update later Writing Your Program Defining Functions def main print Hello world Name the function for the purpose you wrote it for Don t forget to indent the instructions that go inside the function Argument A value passed to a function or method assigned to a named local variable in the function body Ex def addUp a b print this is a b a b a and b are the parameters 1 and 3 are the arguments we passed in The function outputs this is 1 3 4 http docs python org glossary html glossary Calling Functions main will give the output Hello world There is no colon when calling a function Use colons with def Try this yourself Output E g Print print Hello world will give the output Hello world Similar formatting different output print Hello world will output Hello world will output Helloworld print Hello world Similar formatting different output print Hello print world print print Hello print world print will give the output will give the output Hello world Hello world Data Types The data type of an object determines the values it can hold and the operations which can be performed on it Numeric Data Numeric data comes in 2 main flavors Integers whole numbers 2 5 7 etc Floating Point Numbers non integers 0 2 5 125 etc CS108 Notes Prof Aaron Stevens Data Types Non numeric Data Types Those include strings text lists dictionaries etc Basically anything you can not add up using a simple plus sign Not a String Not a Problem You can also format outputting variables you ve defined x 42 will give the output The value of x is 42 print The value of x is x Not a String Not a Problem x 42 print x causes an error So what do we do x 42 print str x will give the output 42 Defining Variables Rules for naming variables Have to start with a letter or underscore Can contain letters numbers and underscores Can t contain spaces punctuation etc Can t be Python keywords Are case sensitive Defining Variables Things that aren t rules but are worth considering You should give your variables sensible names price pixelColor or samplingRate instead of x Just because you technically can start your variable names with underscores doesn t mean you should Defining Variables For multi word variable names two options start capitalizing each word after the first myCar separate words with underscores For instance a variable for Ford Focus could be my car Abbreviating is common for longer words So a variable for average price could be avgPrice or even avg Variables Variables can hold all kinds of values including strings different types of numbers and user input To assign a string value to a variable you have to wrap the string in quotes like usual firstName John lastName Doe mathProblem 5 5 print lastName firstName mathProblem will give the output Doe John 5 5 Variables Variables can also be assigned new values that are relative to their old values For example total 10 print Original total total total total 4 print New total total will give the output Original total 10 New total 14 Variables Remember A variable has to have been defined on a previous line before it can be used on the right hand side of an equation so total total 4 print Total total causes an error since there was no mention of the value of total before the line trying to redefine it Numeric Operators Python built in numeric operators addition subtraction multiplication division exponentiation remainder modulo CS108 Notes Prof Aaron Stevens Python Arithmetic Try writing the following code in your program area and see what it outputs Def main a 12 b 2 c 16 d 3 e 2 5 print the value of a is a print a b 5 print a b d print a b d print b d print c e a a b print the value of a is a Python Arithmetic Is this what you got the value of a is 12 30 18 42 8 13 5 the value of a is 14 Exercise Time Write a program that takes in a birthday dd mm yy and returns The age Number of days until next birthday Taking User Input Sometimes
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