South Metro High School Chapter
Oct. 3, 2017

{code}

agenda

  • intros

  • 4 universal ideas pt. 1

  • brain break!!!

  • 4 universal ideas pt. 2

  • pomodoro* 1

  • pomodoro 2

 

*what's a pomodoro?

Shelly Sousa

@ Girls in STEM: Board Co-Chair
@ ViaSat Inc.: Business Systems Analyst
     also: ViaSat STEAM Program Champion, Women in
     Technology board member

 

Michelle Lim

@ Girls in STEM: Middle School Program + Website
@ mmmanyfold: Co-Founder + Full-Stack Developer
@ KidsTek: Teaches "Intro to Programming" elective at Hinkley High School

“Computer science is as much about programming as astronomy is about telescopes”
-Mike Fellows

 

 

Remember...
Computer systems are designed by humans to serve human (/animal/environmental) needs.

This is what I tell people who ask for advice about starting (or pivoting) their career in tech. “Be good at being bad at things,” I say. “You’ll have no idea what you’re doing, so you’ll just keep learning. You won’t get to be the best at everything or even most things or even some things. It’s not possible, and it’s not just you. So get good and comfortable having no idea, but figure out ways to get closer to having an idea.”

 

–Gina Trapani, Partner & Director of Engineering at Postlight.
Founded ThinkUp, Makerbase, Todo.txt, Lifehacker.

universal ideas

in all

"Turing-complete"
programming
languages

4

the following examples use Python3 (for simplicity), but the ideas are not limited to one language!

disclaimer:

first, let's open our programming environment:
https://repl.it/languages/python3

resize the windows so this can be right next to the slides

when you see this:

this is a code block

try typing the code yourself in the left pane of repl.it

when you see this:

code block

it means go ahead and RUN your program
(click the play button)

storing & retrieving data

1

aka

"variables"

variables

...can be thought of as containers that hold information (data).

 

Their sole purpose is to label and store data in computer memory.

 

This data can then be used and changed throughout your program.

variables

You can re-define a variable, and/or manipulate it in place, over and over again.

Type this in repl.it (left pane): 

x = 0           
x = x + 1
x = x + 1
x = x + 1

Q1: What will be the final value of x?

variables

x = 0           
x = x + 1
x = x + 1
x = x + 1

print(x)

A: add this print() function at the end & then run it to see if you're right

variables

we can also do this with strings!
(a sequence of characters)

 

Type this in repl.it (left pane):

name = "Wendy"           
name = name + " Merchant"
name = name + ", P.E."

Q2: What will be the final value of name?

Variables

 

name = "Wendy"           
name = name + " Merchant"
name = name + ", P.E."

print(name)

A: add this print() function & then run it to see if you're right

Variables

Types of values include:​​

 

  • String                         "Wendy"

  • Integer (whole #)     -4

  • Float (decimal #)      5.01248

  • Array (list)                  ["Wendy", -4, 5.01248]

  • Boolean                     True or False

manipulating data

2

via

"inputs" & "outputs"

input

...is a piece of data that goes in to a program.

 

The program does something with it, and often (but not always) spits out an...

output

demo:

ascii art generator

input

output

program

cat.jpg

text

demo:

ascii art generator

How does this work??

 

RGB sensors (cones) in the human eye - we have a few million of these, which are equivalent to megapixels

where else is this applied?

artificial intelligence:
"computer vision"
photobooth effects
SNAPCHAT!!!

all made possible by...

functions

strings, integers, and variables are like nouns. they just exist.

a function is a verb. it does things!

 

Let's define a simple greeting function:


def greet(name):
   print("Hi " + name)

defining a function


name of
our function

in parentheses, we name our "arguments" - any input values our function will need in order to run

everything after the first line is what the function will do, when it's "called"


def greet(name):
   print("Hi " + name)

calling a function

 

this part "calls" the function, telling it to actually execute


def greet(name):
   print("Hi " + name)

greet("Shelly")

try running this!

functions within
functions

BTW, print() is also a function - it comes built in with Python :)


def greet(name):
   print("Hi " + name)

functions in ascii-art.py

   scale_image(image, new_width=100)
    # resizes an image
   convert_to_grayscale(image)
    # converts image to grayscale
   map_pixels_to_ascii_chars(image, range_width=25)
    # maps each pixel to a character based on its  
      number range. 0-255 is divided into 11 ranges
      of 25 pixels each

   convert_image_to_ascii(image, new_width=100)
    # calls all of the functions above in a specific
      order, resulting in a string of characters

   handle_image_conversion(image_filepath)
    # calls convert_image_to_ascii (above) on the
      image file provided
#!/usr/bin/env python

# this script converts an image to ascii art
# adapted from https://www.hackerearth.com/practice/notes/beautiful-python-a-simple-ascii-art-generator-from-images/

# must have PIL or Pillow installed
from PIL import Image

ASCII_CHARS = [ '#', '?', '%', '.', 'S', '+', '.', '*', ':', ',', '@']

def scale_image(image, new_width=100):
    # resizes an image, slightly adjusting the aspect ratio.
    
    (original_width, original_height) = image.size
    aspect_ratio = (original_height/float(original_width)) * .5
    new_height = int(aspect_ratio * new_width)

    new_image = image.resize((new_width, new_height))
    return new_image

def convert_to_grayscale(image):
    return image.convert('L')

def map_pixels_to_ascii_chars(image, range_width=25):
    # maps each pixel to an ascii char based on the range in which it lies.
    # 0-255 is divided into 11 ranges of 25 pixels each.

    pixels_in_image = list(image.getdata())
    pixels_to_chars = [ASCII_CHARS[pixel_value//range_width] for pixel_value in
            pixels_in_image]

    return "".join(pixels_to_chars)

def convert_image_to_ascii(image, new_width=100):
    image = scale_image(image)
    image = convert_to_grayscale(image)

    pixels_to_chars = map_pixels_to_ascii_chars(image)
    len_pixels_to_chars = len(pixels_to_chars)

    image_ascii = [pixels_to_chars[index: index + new_width] for index in
            range(0, len_pixels_to_chars, new_width)]

    return "\n".join(image_ascii)

def handle_image_conversion(image_filepath):
    image = None
    try:
        image = Image.open(image_filepath)
    except Exception as e:
        print("Unable to open image file {image_filepath}.".format(image_filepath=image_filepath))
        print(e)
        return

    image_ascii = convert_image_to_ascii(image)
    print(image_ascii)

if __name__=='__main__':
    import sys

image_file_path = "karen.jpg"
handle_image_conversion(image_file_path)

brain break!!!

control flow

3

via

"if/then/else"

go to example:

repl.it/Lsss/latest

iteration

4

aka

"looping"

while 0 == 0:

  choice = input("\nReply 1 if you'd like to learn more about 'if statements'. Reply 2 if you'd rather not.\n")
  
  if (choice == "1"):
    print("\nAn 'if statement' takes a certain test (in this case: is 'choice' equal to 1?) and acts based on the 'truthiness' of that test. Truthiness is a funny word that basically refers to a Boolean - a binary variable, having two possible values: 'true' or 'false'. It's named after the mathematician George Boole. Thanks to 'if statements' and Booleans, our code can have many alternate universes...")
  
  elif (choice == "2"):
    print("\nMeow")
    
  elif (choice == "hi"):
    print("\nwell hello there")
  
  else:
    print("\nNot a valid response!")

now add this line at the beginning, and indent the rest

SHORTCUT:
select everything
+ press tab
(to indent all
at once)

the while loop

examples:


"count to x"
https://repl.it/LyC4/latest
 

"5 yr old brother"
https://repl.it/LyGa/latest

Now that you have learned about coding

 

What can you do with it?

Careers in Coding

   
   1) Front-End Developer
         develops the part of an application that the user can see and 
          interact with (html/css, javascript)
   2) Back-End Developer
       develops the part of an application that handles logic, database  
          interactions, user authentication, server config. (sql, python)
   3) Full-Stack Developer
       a front-end and back-end developer who codes in multiple languages   
          and understands how application servers communicate (http, REST)
   4) Data Scientist / Engineer
          analyzes data, finds patterns, illustrates with pics (statistics)
   5) UX Designer
          makes apps easy for people to use (graphics, layouts, clicks)

coding career IRL example

 


 

https://www.exede.com/contact-us-exede

Or you could play music with fruit...

& encrypt secret messages...

https://repl.it/KoWe/latest

Let's go!

GSTEM HS Coding 10/3

By Michelle Lim

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GSTEM HS Coding 10/3

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