introduction to: python and opensesame part i. python a high-level programming language it can do a...

Introduction to:Python and OpenSesame

Part I

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Python

• A high-level programming language• It can do a lot of things• We will use python in this course in the

context of in-line scripting for opensesame.• For that, you need to know how to write basic

scripts.

Intro to: Python and OpenSesame

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Python

Intro to: Python and OpenSesameFrom: XKCD comics

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Python Shell


Start -> python -> Python GUI (IDLE)

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Python Shell

• An Interpreter:– You write a line of code– Python interprets it and executes it

• Try:– 1+1 [addition]– 5*2 [multiplication]– ‘hello’ [string]


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Python Basic (Data) Types

• INT (integer) – 2,3,0,15,100000• FLOAT (floating point) – 2.0, 3.5, 0.12, 100.999• STR (string) – ‘Hello’, ”to you all”, ‘1+1’, “11”

• Use type(…) to check:– 2– 2.2– ‘2.2’


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Variables (assign value to variable)

• X = 1; Y = 2.0; Z1 = ‘Gevald’; Z2 = ‘avoi’• Operations on variables? No problem:• X+Y [int+float = float]• X/Y [/ = devision, // = int devision]• Z1+X [int+str = error]• Z1 + Z2 [str+str = str]• Z1*3 [str*int = str (overloaded?!)]• Z2*Y [str*float = error]


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Variables (jumping from types)

>> x = 2.0; y = 3>> int(x)2>> str(x)‘2.0’>> float(y)


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Variables (pointing)

>> x = 1; y = 2

>> x = y; x is y?


x 1( memory location: 112125123)

y 2( memory location: 112125125)



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Variables (pointing) - continue

>> y = 1

>> x is y ?




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Functions - BASICS


BLACK BOXINPUT OUTPUT

String:“Hello World” print(“Hello World”)

Hello World

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Script!

A text file (.py) with python instructions for the interpreter. No more one liners!

In Python Shell:File -> New File

In the new File:File -> Save As.. -> example.py


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Script!

Super text files! Special language keywords are highlighted in different colors.


Example

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Your first Python program

In a new file (Call it first.py)

1. Create a program that saves the phrase: ‘hello world’ in a variable called phrase.

2. Use the print function to print the content of phrase.

3. Execute your program


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Back to functions

Recall: input -> blackbox -> output

Python comes with many built-in functions.

For more information, visit the official documentation:https://docs.python.org/2/library/functions.html


https://docs.python.org/2/library/functions.html

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Back to functions

Examples:>> len() # returns the length of the input>> abs() # returns the absolute value>> round() # rounds to the nearest integer >> raw_input() # takes user input as str


Notice I’m using # (hash .mark) for comments.

Python ignore everything after this symbol, but you

shouldn’t!

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Python Standard Library

But the built-in functions are limited, and Python has MUCH MORE to offer in the Python Standard Library (https://docs.python.org/2/library/index.html)

The python standard library has many modules (script files and folders) with many useful functions that are readily available – once imported.


https://docs.python.org/2/library/index.html

https://docs.python.org/2/library/index.html

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Python Standard Library - Modules

Math>> import math>> help(math) # lists all the available functions

To use a function:>> math.sin() # The sine function>> math.factorial() # the factorial (עצרת) function

(also has some special variable values like math.pi)


The dot stands for from, as in: use sin

from math

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Python Standard Library - Modules

>> Import random>> random.random()

if you only plan on using one function from a module:

>> from random import random>> random()


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More Python libraries

Python has even more libraries available on the web which you could download and use.

We will not cover these in this class, but feel free to explore: numpy, matplotlib and more..(Talk to me later if you want to learn more about this)


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Objects – Tip of the iceberg!

Traditionally, this part comes much later in the learning process. But, it is essential for OpenSesame scripts and I believe the tools which it provides will help learning the other stuff.

Everything in Python is an object. This is what makes Python an OOP [Object Oriented Programming] language.

What is an “OBJECT”?


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Objects are blueprints


Roof

Door

Chimney

Handle

Address Owner #Rooms Color Who lives there?

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We can create an instance of an object:

>> house1 = house()

We can add properties to it:

>> house1.address = ‘Ragar 19, Be’er Sheva’>> house1.price = 100000>> house1.roof_color = ‘pink’


These Belong EXCLUSIVELY to the house1 instance of the house object

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Methods

• Objects have functions – called Methods• Methods are functions that belong to the object

type.

>> house.colorPink>> house.repaint(‘yellow’)>> house.coloryellow


Just an in object variable

a method, notice the parenthesis.

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Methods

We said everything in Python is an object.Int, float, str are objects too!

st = ‘stringy‘ # Creating a string instancest.strip(‘y‘) # Using the strip method

Ask for help! Use help(str) to learn all the str methods


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Importing new objects!

Similar to functions, we can import new objects from the Python Standard Library.

We will now import the turtle library.


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Turtle

Turtle is based on an old children’s programming language called “Logo”.

we will use turtle throughout the course to visualize everything we learn!

(This approach will also help us with OpenSesame inline which uses objects all the time!)


** Some of the examples in this part were adopted from the Udacity Object Oriented Programming – Python course

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Turtle – How it works


(0,0)

Move Forward, 100 steps

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Turtle - setup

First, we need to import the turtle module which has all the code for the needed objects.

** note: to make sure turtle works well, write all the code in script files and NOT in the shell.

I still use >> to indicate that it’s a line of code.

>> import turtle

We will need two objects1. A screen object2. A turtle object


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Turtle – Screen Object

>> import turtle>> window = turtle.Screen()

We created a new Screen instance called window Let’s use methods to change its appearance and behavior:

>> window.bgcolor(‘red’) # sets the background to red>> window.exitonclick() # sets the close window properties


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Turtle – Turtle Object

>> yoni = turtle.Turtle()

What can yoni (turtle instance) do?

>> yoni.forward(100) # Go forward, 100 steps!>> yoni.right(10) # Turn right, 10o !


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Time for a Python Program

In a new file (call it, square.py)Use the turtle object to draw a square!

Don’t forget to create a window instance and use the exitonclick() method in the end of the script


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Another type, Bool (Boolean)

• Bool is a True/False type• It is the basis of conditioning• You get a Boolean value for these type of

statements:– 1000 > 999– ‘aaa’ == ‘bbb’– 1 in (1,2,3,4)– and more [ >=, <= , != ]


Use the type() function to on the

input True

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Conditionals

• Sets conditions to the program in the form:


if <this == True>:<do that>

Condition

Colon

Indentation

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Conditionals

• Example:

>> x = 5>> y = 6>> if x > y:>> print(‘x is bigger than y’)


Where is the <True> ?

x > y is True!== True is embedded

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Conditionals – what else?

• We can create more advanced conditions:

if 1 > 2:print(‘a new fact!’)

else:print(‘The world is in order’)


NOTE: Code blocks (after a colon) are indented. We can have multilevel Indentation

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Conditionals – what else?

• And even more advanced conditions:

if 1 > 2:print(‘1 > 2’)

elif 2 > 1:print(‘2 > 1’)

else:print(‘Chaos!’)


POP QUIZ: What will be the output?

1. 1 > 22. 2 > 13. Chaos!4. True5. False6. Error

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Logical Operators (AND / OR)

x = 1; y = 2; z = 3

if x == 1 and y == 2:print ‘ok’

if y == 2 or z == 4:print ‘no worries’


AND – True if:Both are true

OR –True if:1 is true, 2 is true, both are true

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Time for a Python Program

In a new file (call it, conditions.py)Write a program that:1. Sets x and y to be either 1 or 2 randomly.2. If x is bigger than y, draw a square with turtle3. If y is bigger than x, draw a circle with turtle4. If x and y are equal, draw a line with turtle

Hint: Use the choice() function from the random module, it takes as input a number sequence from which it draws a choice (1,2).Also, turtle has a draw circle function, find out what it is.


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