Understanding Variables in Python Programming: Basics and Best Practices

Student objective: How are variables set up and used in programming? Bell ringer: Where we using python in the interactive mode or script mode on Friday?

Set Up Grade Sheet • KWL (5) • Syllabus (5) • Communication compact (5) • Computer Parts Project (25) • Vocab (10) • Print Project (10) • Number Guessing Game (10)

Agenda • Notes on python basics and variables • Assignments: programming

Bell Ringer Answer: Interactive Interactive mode-program and run in IDLE • Immediate feedback • Not designed to save and run later Script Mode Write the program • Write program and save it to use later

Let’s try it • To write a python program and save it: • Open Python IDLE • Click on file—New Window • Type your program in • File—Save as .pyin documents folder of python • Click Run—Run Module • IDLE pops back up with program

Syntax Errors • Spelling/grammar • Picked up prior to running program

Runtime errors • Occur during execution of program • 4-line error message starting with Traceback • Tells where the error is and what it is

Semantic errors • Don’t use commas with numbers or will get this error • Code will run but be wrong

Computer • Input • Processing • Output

Variables Variables (values) • Integers: int numbers no decimal points • Strings: str use singleor double quotation character or string of characters: letters, numbers, punctuation • Long string: str multi-line string: triple quotes • Floating point: float decimal numbers

Color coding • Special words, like print: orange • Strings: green • Output: blue • Comments: red

Comments • Used to explain code • Invaluable to programmers • Are not executable by the computer • # symbol is used to denote the start of a comment

Blank Lines and Spacing Blank lines • Are ignored by the computer • Can make program easier to read Spacing • is critical and will create errors if not followed • Tells where blocks of code start and where they stop • Convention: 4 spaces in • Necessary for if statement

Naming Variables • If you don’t know the type of variable, you can find out by • Writing in the IDLE: • type ( variable ) then click return (Remember strings in quotes, numbers not) • You can name variables (words, numbers) to input into memory (Name it so you can use it) • Teacher = “Mr. Morton” • First = 5 • *You can have more than one name for one thing • *You can also change names

Rules for naming variables: • Can use letters, numbers and underscore character(_) • Case sensitive • Must start with letter or underscore (Not a good idea to start with underscore), NOT A NUMBER • Make variables names clear—don’t try to abbreviate

Concatenate: • Adding strings like “cat” + “dog” • Results would be catdog

Using variables • Variables can also be made to equal themselves: • >>Score = 7 • >>Score = Score • >>Score = Score + 1 • >>print Score Hit return • Generates >>8 • Useful to increment or decrement a value

Understanding Variables in Python Programming: Basics and Best Practices