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Saturday, May 4, 13

Juan GomezCo-Founder of PyhtonKC

Twitter: @_juandg

Teach your kids how to program with Python and the Raspberry Pi

Saturday, May 4, 13

May the 4th be with you!Saturday, May 4, 13

So what is this talk really about?

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Brief History of the RaspberryPiMore at: https://www.youtube.com/watch?v=z-j4USHTLWM

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What you’ll need:

• MicroUSB Power Supply• SD Card (>= 4GB)• USB Keyboard• USB Mouse• Ethernet Cable• HDMI Cable• Monitor• Case?• HDMI to VGA Adapter?• USB WiFi Adapter?• USB to TTL Cable?• RCA Cable?

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How do you teach kids?

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Make it fun!http://www.adafruit.com/products/975

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Some tips

• Seriously, Make it fun!

• Start with Math

• Be Patient

• Explain the Basics

• Use real life examples

• Kids are slow typists!

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How do I set it up?

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Disclaimer

• This an intro to Python for YOU, not your kids.

• The kids version is at: https://github.com/mechanicalgirl/young-coders-tutorial

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A Python Code Sample

x = 34 - 23 # A comment.

y = “Hello” # Another one. z = 3.45

if z == 3.45 or y == “Hello”:

x = x + 1

y = y + “ World” # String concat.

print x

print y

Saturday, May 4, 13

Enough to Understand the Code

• First assignment to a variable creates it • Assignment is = and comparison is ==• For numbers + - * / % are as expected

• Special use:• + for string concatenation• % for string formatting (as in C’s printf)

• Logical operators are words (and, or, not) not symbols (&&, ||, !).

• The basic printing command is print

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Comments

•Start comments with #, rest of line is ignored•Can include a “documentation string” as the first line of a new function or class you define•Development environments, debugger, and other tools use it: it’s good style to include one

def my_function(x, y): “““This is the docstring. This function does blah blah blah.”””# The code would go here...

Saturday, May 4, 13

Python and Types

•Everything is an object!

•“Dynamic Typing”-> Data types determined automatically.

•“Strong Typing” -> Enforces them after it figures them out.

x = “the answer is ” # Decides x is string. y = 23 # Decides y is integer. print x + y # Python will complain about this.

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Basic Datatypes

• Integers (default for numbers)•z = 5 / 2 # Answer 2, integer division

• Floats•x = 3.456

• Strings• Can use “” or ‘’ to specify with “abc” == ‘abc’• Unmatched can occur within the string: “matt’s”• Use triple double-quotes for multi-line strings or strings that

contain both ‘ and “ inside of them: “““a‘b“c”””

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Whitespace

Whitespace is meaningful in Python: especially indentation and placement of newlines•Use a newline to end a line of code

Use \ when must go to next line prematurely

•No braces {} to mark blocks of code, use consistent indentation instead

• First line with less indentation is outside of the block• First line with more indentation starts a nested block

•Colons start of a new block in many constructs, e.g. function definitions, then clauses

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Assignment

•You can assign to multiple names at the same time >>> x, y = 2, 3

>>> x

2>>> y

3

This makes it easy to swap values>>> x, y = y, x

•Assignments can be chained>>> a = b = x = 2

Saturday, May 4, 13

A Python Code Sample x = 34 - 23 # A comment.

y = “Hello” # Another one. z = 3.45

if z == 3.45 or y == “Hello”:

x = x + 1

y = y + “ World” # String concat.

print x

print y

Saturday, May 4, 13

Side by Side with Java

Java (C#) Pythonpublic class Employee{ private String myEmployeeName; private int myTaxDeductions = 1; private String myMaritalStatus = "single";

public Employee(String EmployeName) { this(EmployeName, 1); }

public Employee(String EmployeName, int taxDeductions) { this(EmployeName, taxDeductions, "single"); } public Employee(String EmployeName, int taxDeductions, String maritalStatus) { this.myEmployeeName = EmployeName; this.myTaxDeductions = taxDeductions; this.myMaritalStatus = maritalStatus; }}

class Employee():

def __init__(self,

employeeName

, taxDeductions=1

, maritalStatus="single"

):

self.employeeName = employeeName

self.taxDeductions = taxDeductions

self.maritalStatus = maritalStatus

Saturday, May 4, 13

Life is Short(You Need Python)

- Bruce Eckel (Thinking in C++)

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Useful books:

Python for Kidshttp://oreil.ly/10boyUq

The Quick Python Book, 2nd Edhttp://amzn.to/lXKzH5

Google's Python Classhttps://developers.google.com/edu/python/

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Let’s start by writing text based games

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A Skeleton• Let’s start with the most basic pygame program

template.pytemplate.py123456789

1011121314151617

from pygame import *from pygame.sprite import *from random import *

init()

screen = display.set_mode((640, 480))display.set_caption('Window name!')

while True: e = event.poll() if e.type == QUIT: quit() break

screen.fill(Color("white")) display.update()

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Surface• Most of the game elements you see are represented as Surface

• display.set_mode((x, y)) creates your canvas – it returns a Surface object

Useful surface methods:• fill("color") fills the surface object it's been called from

• blit(surface, area) paints the source surface onto the rectangle bounded by the area tuple–Example: screen.blit(ball, (50,50))

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Rect• Objects that store rectangular coordinates

• Call .get_rect()on a surface to get its bounding box

Rectangle methods/variables:• .center holds the object's center as a tuple

• .colliderect(target) returns True if the parameter overlaps with the object

• .collidepoint(target) returns True if the target point overlaps with the object

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Media• Loading an image:–img = image.load("file.gif").convert()

• Getting a bounding rectangle:–img_rect = img.get_rect()

• Loading and playing a sound file:–mixer.Sound("file.wav").play()

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Sprite• Simple base class visible game objects inherit from.

Ball.pyBall.py123456789

1011

from pygame import *from pygame.sprite import *

class Ball(Sprite): def __init__(self): Sprite.__init__(self) self.image = image.load("ball.png").convert() self.rect = self.image.get_rect()

def update(self): self.rect.center = mouse.get_pos()

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Using Sprites• They're just objects: initialize them–ball = Ball()

• Create a group of sprites in main–sprites = RenderPlain(sprite1, sprite2)

• Groups know how to draw and update–sprites.update()

–sprites.draw(surface)

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Events• User input such as clicking, moving mouse or key presses

• Add more branches to test the result of event.poll()

• Events to test for:–QUIT–MOUSEBUTTONDOWN–JOYBUTTONDOWN

• Testing for the letter ‘d’ being pressed using KEYDOWNif e.type == KEYDOWN:

if e.key == K_d: …

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Adding Text• f = font.Font(font, size) goes before your game loop

– Example: f = font.Font(None, 25) – Usually, None is a good enough font!

• text = Font.render(text, antialias, color)– Example: text = f.render("Hello!", True, Color("green"))

– Returns a surface

• Must be blit, just like any other surface– Example: screen.blit(t, (320, 0))

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Let’s dissect a game!

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Join PythonKC -> http://www.meetup.com/pythonkc/

Saturday, May 4, 13

Juan GomezCo-Founder of PyhtonKC

Twitter: @_juandg

Thanks!

Saturday, May 4, 13

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Saturday, May 4, 13