IPython notebook Utah_Workshop/Utah_Notebooks/01-Intro-to-Python/Lesson_02_MorePython-student.ipynb

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Utah_Workshop/Utah_Notebooks/01-Intro-to-Python/Lesson_02_MorePython-student.ipynb

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Kernel: Unknown Kernel

Looping through your list

make a new list of stuff

your name
favorite fruit
favorite number
favorite animal
number of siblings
favorite musician

eg. mybag = ['cindee', 'blueberry', 13, 'cat', 1, 'Lorde']

In [1]:

mybag = ["black apple", "Danny", "Pops","Smurfette", 2134567890876543213456789]
print mybag

Out[1]:

['black apple', 'Danny', 'Pops', 'Smurfette', 2134567890876543213456789L]

I want to refer to each item in my bag and tell you what it is

to do this I use a for loop

There are two important parts:

: colon at the end of the line
indent so python knows this is the activity at each pass

for thing in mybag:
    print thing

In [ ]:

# thing is just a temporary variable , holding one of the items for a short time

#Asking questions about things in our bag ##Sometimes we want to check the things in our bag

is my name in the bag? (what about misspelling?)
is there a cat in mybag?

In [8]:

for i, thing in enumerate(mybag):
    print i,thing

Out[8]:

black apple
Danny
Pops
Smurfette
2134567890876543213456789

In [ ]:

# I can check if something specific is in my bag

Booleans?

True and False are a special type of object called Booleans

True and False are used in comparisons.

isinstance

We can use a special function called isinstance, to check if something is a string or a number

for strings use: str (short for string)
for numbers use: int (short for integer)

In [ ]:

type("wendy")

In [ ]:

# finding a type
type(3)

Exercise

See if the third thing in your bag is a number

In [9]:

isinstance(3, int)

Out[9]:

True

In [10]:

a = 1
b = a
b==a

Out[10]:

True

Lets combine looping, and questions

We can loop through the things in our bag
Check if the thing is a string (use isinstance and str to make this comparison)
print the thing if it is a string

In [18]:

for thing in mybag:
    print thing, 'is an int?',isinstance (thing, int)

Out[18]:

black apple is an int? False
Danny is an int? False
Pops is an int? False
Smurfette is an int? False
2134567890876543213456789 is an int? False

Multiple Dimensions

##What if we combined everyones bag into one bigbag?

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##How do I access all the favorite animals?

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mean = 2

mean=[]

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# I wished that worked, now what do I do?

#import and arrays

import

Python comes with a bunch of cool tools, but sometimes I need other tools (like above)

To get access to these tools I need to import them into my Python workspace

##arrays

One set of tools comes in a package called numpy
Numpy is used in data science all the time, because it allows us to easily work with lists of lists efficiently.
These objects are called arrays

Import numpy to use arrays

lets import numpy
we can even give it an alias or nickname

In [ ]:

import numpy
import numpy as np

In [21]:

# np.asarray

arr = np. asarray(mybag)

In [23]:

#print bigbag

arr.dtype

Out[23]:

dtype('S25')

In [33]:

ones = np.arange(25)
ones.shape = (5,5)

In [ ]:

ones

In [2]:

ones [1:,3]

Out[2]:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-792c3430596c> in <module>()
----> 1 ones [1:,3]

TypeError: 'function' object has no attribute '__getitem__'

Images as Arrays

Now that you have exposure to arrays, lets think about how a two-dimensional array can introduce us to image processing.

Many images you see on the web are just arrays of color values, but at such a low resolution, it blends together into a smoth image.

Mona Lisa

Consider the images below.

One looks like the painting
The other looks like an array of colors
Squint your eyes, how does this impact the image on the right?

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In [28]:

ones

Out[28]:

array([[ 1.,  1.,  1.],
       [ 1.,  1.,  1.]])

In [ ]:

When we look into face detection, I want you to think of all the images as arrays of colors.

#Visualizing multiple dimensions using ipythonblocks

Our next session will help us get better acquianted with thinking about indexing into arrays and images as arrays. ##ipythonblocks ipython blocks allow us to understand this complex structure of multidimensional objects a little more easily

Lets create a simple set of blocks that has 4 rows and 4 columns

Colors

Colors are represented as RGB triplets

each value can range from 0 -> 255
0 is black
255 is a fully saturated color

In [43]:

from ipythonblocks import BlockGrid
# define some colors  (R, G, B) or (red, green, blue)
black = (0, 0, 0)
violet = (132, 23 , 54)
orange = (255, 123, 34)
red = (255, 51, 51)
yellow = (255, 255 , 0)
blue = (51, 51, 255)
green = (51, 255, 51)
indigo =(102, 0, 204)
# make a black grid
blocks = BlockGrid(10,10, fill=black)


blocks[0,1:9] = red
blocks[1:,0] = red
blocks[1:,9] = red
blocks[1,1:9] = orange
blocks[2,1:9] = yellow
blocks[3,1:9]= green
blocks [4,1:9] = blue
blocks [5,1:9] = indigo
blocks [6,1:9] = violet
blocks [7,1] = red
blocks [7,2] = orange
blocks [7,3] = yellow
blocks [7,4] = green
blocks [7,5] = blue
blocks [7,6] = indigo
blocks [7,7] = violet
blocks [7,8] = red
blocks [8,1] =red
blocks [8,2] = orange
blocks [8,3] = yellow
blocks [8,4] = green
blocks [8,5] = blue 
blocks [8,6] = indigo
blocks [8,7] = violet
blocks [8,8] = red
blocks [9,1] = red
blocks [9,2] = violet
blocks [9,3] =indigo
blocks [9,4] = blue 
blocks [9,5] = green 
blocks [9,6] = yellow 
blocks [9,7] = orange 
blocks [9,8] = red


# show the grid
blocks

Out[43]:

In [ ]:

# Once you have created the block
# use your mouse to hover over each block, what does it tell you?

In [57]:

blocks = BlockGrid(4,4)
previous_block = None
for block in blocks.animate(0.8):
    block.rgb=red
    if previous_block:
        previous_block.rgb = black
    previous_block = block

Out[57]:

In [58]:

# we can make a whole column red
blocks = BlockGrid(4,4, fill=black)
blocks[:,2] = red
blocks

Out[58]:

###Exercise:

Can you make the blocks and make the whole 2nd row red and everything else black?
what other shapes can you come up with?

In [ ]:

Advanced

Using math to generate images.

In [3]:

from ipythonblocks import BlockGrid
import math

math.fabs?

In [34]:

w = 20  # width of grid
h = 20  # height of grid
r = 3   # minor radius (size of inner ring)

grid = BlockGrid(w, h, block_size=8)

Equation for Torus

c = radius form center of hole to center of torus tube
a = radius of the tube
x = x coordinate
y = y coordinate

ParseError: KaTeX parse error: {align} can be used only in display mode.

In [59]:

## Lets Draw the Torus

for block in grid:
    # Color value is set by location on the torus
    val = math.fabs(math.sqrt((w / 2. - block.col) ** 2 + (h / 2. - block.row) ** 2) - r) ** 2 / r * 255
    #print block.row, block.col, val
    block.red = val
    block.green = val
    block.blue = val

print grid

Out[59]:

BlockGrid
Shape: (20, 20)

In [60]:

grid

Out[60]:

Can you manipulate the parameters to change the torus?

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