Guide to Programming with Python

1. Guide to Programming with Python Chapter One Getting Started: The Game Over Program

2. Fm: http://xkcd.com/353/

3. Objectives • Introduce Python • History • High-level language (computer program & algorithms) • Interpreted language • Get started with Python • Python installation • Statements (e.g., print text to the screen) • Comments & application • Demonstrate Python’s development environment, IDLE: iterative / script modes Guide to Programming with Python

4. Hello World / Game Starts • “Hello World” program: By tradition, prints "Hello, world!” • Often used as first program • print “Hello world” • Console window: Provides a text-based interface to Windows operating system • Terminal application: Provides a text-based interface to Mac OS X and Linux operating systems Guide to Programming with Python

5. Introducing Python • Powerful yet easy to use programming language (platform independent) • Developed by Guido van Rossum • First released in 1991 • Named after comedy troupe Monty Python • Getting more popular • Python is free and open source • Has strong community • High-level programming Language • Interpreted language • Object oriented (image: stock.xchg, No.655639) Guide to Programming with Python

6. Algorithms & Computer programs • An algorithm is a set of well-defined instructions for accomplishing a task (e.g., S’mores algorithm for making s'mores) • When we write computer program, we are generally implementing a method (an algorithm) devised previously to solve some problem. • A computer program is a sequence of instructions that are executed by a CPU • Computer programs can be written in high-level (e.g., Python, Perl, C, C++, Java), or primitive programming languages Guide to Programming with Python

7. High-level Programming Language • High-level programming languages separate from the low-level processor operations; closer to human language than machine language (machine code or machine language, a system of instructions and data executed directly by a computer's central processing unit, CPU.) • This greater abstraction and hiding of details is generally intended to make the language user-friendly ("Programming at the speed of thought”), but maybe less efficient (but it is not a big problem in many cases with powerful personal computers) Guide to Programming with Python

8. Python Is a “Glue” Language • Can be integrated with other languages • C/C++ • Java • Use existing code • Leverage strengths of other languages • Extra speed that C or C++ offers Guide to Programming with Python

9. Python is Interpreted Language • A python program is just a text file; How can a computer know what to do? Different models of execution for modern high-level languages • Interpreted • Interpreted languages are read and then executed directly, with no compilation stage. • Examples: Python, Perl, Ruby, Java • Compiled • Compiled languages are transformed into an executable form before running. • Examples: C (and C++) • Comparison of “Hello World” in Python, Perl, and C Guide to Programming with Python

10. Setting up Python • Windows • Linux • Python probably already installed • Test: try running python at command prompt • Mac OS 10.5.x and up • Lion (10.7) Python 2.7.2 installed; IDLE 2.7.2 (http://www.python.org/idle/), Tk version 8.5 • Leopard (10.5.x) already has Python 2.5.1 installed, but you need to install IDLE.app following instructions at http://wiki.python.org/moin/MacPython/Leopard • If not installed, go to http://www.python.org/download/ • Remember: your computer needs a python “interpreter” to understand python codes Guide to Programming with Python

11. Introducing IDLE • Integrated Development Environment (IDE): Application that helps software developers write programs • Like a word processor for your code • IDE that ships with Python • Has two “modes”: Interactive and Script (see demo) • But using which editing program (IDLE, or whatever) is really personal taste. Guide to Programming with Python

12. Interactive and Script Mode • Iterative mode: You tell Python what to do, and it will do it immediately • Script mode: You write, edit, load, and save python programs (just like you write a document in Word processor, and any other types of text processors). But definitely you do not want to write your Python codes with Word! Guide to Programming with Python

13. Programming in Interactive Mode • Great for immediate feedback • Test a simple idea • Remember how something works • Open Python in interactive mode • In Windows, from the Start menu, choose Programs, Python <version>, IDLE (Python GUI) • On STC Lab machines • Windows: Will be in Start menu > All Programs > Departmentally Sponsored > Informatics • Mac: Type python in /Applications/Utilities/Terminal.app or run IDLE.app from the Developer Tools folder in the Dock • Command prompt >>> Guide to Programming with Python

14. Jargon • Statement: Single unit in programming language that performs some action • print "Game Over” • print Statement can display a string (actually, any expression) • String: Sequence of characters • Expression: Something which has a value or that can be evaluated to a single value • "Game Over" • 7 + 2 • Code: Sequence of programming statements Guide to Programming with Python

15. Jargon • Syntax highlighting: Displaying programming code in different colors or fonts, according to the category of each item • Errors • Computers take everything literally • primt "Game Over" produces an Error Message: SyntaxError: invalid syntax • Syntax error: Error in the rules of usage; often a typo (versus logic error) • Bug: Error in programming code Guide to Programming with Python

16. Programming in Script Mode • Great for programs you want to run later • Write, edit, save, and load programs • Like word processor for your programs • Find and replace • Cut and paste • Open a script window • In interactive window, select File menu, New Window Guide to Programming with Python

17. The Game Over Program • Comment: Note in source code meant only for programmers; ignored by computer • Start comment with # • Use opening block of comments • Blank Lines • Also (generally) ignored by computer • Use for readability; keep related code together • Console Window • Final line keeps console window open Guide to Programming with Python

18. Python Is Object-Oriented • Object-oriented programming (OOP): Methodology that defines problems in terms of objects that send messages to each other • dir(1) • In a game, a Missile object could send a Ship object a message to Explode • OOP not required, unlike Java and C# Guide to Programming with Python

19. Summary • Python is a high-level, object-oriented programming language that’s powerful yet easy to use • Python can interface with other programming languages • IDLE is Python’s standard IDE • IDLE has an interactive mode that offers immediate response to Python code • IDLE has a script mode that allows programmers to write, edit, load, save, and run their programs Guide to Programming with Python

20. Summary (continued) • A string is a sequence of characters • A statement is a single unit of programming that performs some action • The print statement displays strings on the screen • An expression is something which has a value or that can be evaluated to a single value • Syntax highlighting is displaying programming code in different colors or fonts, according to the category of each item Guide to Programming with Python

21. Summary (continued) • A syntax error is a violation of the grammar of a programming language; often caused by a typo (we will see logic error) • A bug is an error in programming code • A comment is a note in source code meant only for programmers; ignored by computer  • Comments start with # • You should use an opening block of comments in your programs to identify the programmer, the creation date, and the program’s purpose  Guide to Programming with Python