CS1022 Computer Programming & Principles Lecture 2.2 A brief introduction to Python (2)

Plan of lecture Intro to Portable Python Integrated development environment (IDE) Edit-run workflow From maths to pseudo-code to Python Codecademy Learning to learn What next? CS1022

Portable Python A pre-configured Python distribution Runs directly on Windows from a USB device Portable, lightweight, hassle-free No need to fiddle with class paths, access rights Large set of libraries bundled together No need to get these separately Drawbacks: Only for Windows CS1022

Portable Python (2) We’ll cover the basics of the IDE Editor and edit-run loop Making sense of mistakes Here’s what you should have: Double-click on “PyScripter-Portable.exe” CS1022

Python interpreter pane Portable Python (3) Here’s what you should see: Files pane Editor pane Python interpreter pane CS1022

Portable Python (4) 2 1 3 Basic edit-run loop: What kinds of problems? Load a file Edit it (editor gives feedback) Run it If there are problems, go to 2 else stop What kinds of problems? Program aborts (does not run) Program runs but does not do what we intended 1 2 3 CS1022

Editing a Python program Let’s edit a new Python program: Highlight the text in 2 Delete all of it Type the following in 2 1 2 3 # absolute value n = -20 if n < 0: abs = -n else: abs = n print(abs) CS1022

Running a Python program To run the program we typed, we can: Type <ctrl-F9> or click on green arrow above pane 2 Program will be run in pane 3 CS1022

Running a Python program (2) If we wanted to try the previous program with different values we would have to edit line 1 Instead, we can provide parameters from keyboard CS1022

Editing a Python program (revisited) Let’s edit our Python program and add the following: import “argv” (functionality) from module “sys” from sys import arg # absolute value n = int(argv[1]) if n < 0: abs = -n else: abs = n print(abs) from sys import arg # absolute value n = -20 if n < 0: abs = -n else: abs = n print(abs) Get first parameter and convert it into an integer CS1022

Parameters from keyboard “argv” allows us to read data from keyboard Data are parameters which we assign to variables It is possible to write programs without parameters We need to initialise variables in the program “initialise” = “give initial values” Every time we want to try different values we need to change these This is tedious... CS1022

Parameters from keyboard (2) We need to tell Python we want to use parameters: CS1022

Parameters from keyboard (2) And provide the actual value(s) CS1022

Defining functions By defining a function we can pass parameters from the interpreter line: def absolute(n): if n < 0: abs = -n else: abs = n return(abs) CS1022

Defining functions In the IDE: CS1022

Formatting your program The editor helps you formatting your program Indentations are important! You still need to confirm what the editor does For instance, when the “if” command is finished CS1022

Program with a “for” loop # sum first n integers n = int(argv[1]) sum = 0 for i in range(1,n): sum = sum + i print(sum) CS1022

Program with a “while” loop Let’s write a program to count down from an input n to 0 We must use a while-loop! while condition: statement CS1022

Codecademy You would have been exposed to it by now... It combines Python with “expected outcomes” Compares your program with an expected solution Errors confusing! Plan of topics Gentle, comprehensive Try both: IDE and Codecademy CS1022

Learning to learn How does one learn to program computers? How should we teach programming? Going over syntax, pragmatics and “tricks of trade” Tedious, very time-consuming Different people have different learning pace/speed Hold back or rush people... Route we took: Expose you to basics of a programming language Support and guide you to learn it in your own pace Use existing on-line resources (we cannot compete with them!) This is an opportunity to “learn to learn” A “soft skill” for life Know what you know; know what you don’t know (AND do something about it!) Help is at hand if you have difficulty (demonstrators, lecturers) CS1022

What next? Work your way through lessons and materials on-line Programming is a skill you get by doing Learn with your mistakes (and successes) The more mistakes, the more you learn! Breaking stuff is fun (no-one is hurt, no damages!) CS1022

Further reading Python’s official Web site https://www.python.org/ Wikipedia’s entry on Python http://en.wikipedia.org/wiki/Python Codecademy on-line Python training http://www.codecademy.com/en/tracks/python Python Humour! (who said we are not fun/funny?) https://www.python.org/doc/humor/ Portable Python http://portablepython.com/ CS1022