20장 Py Art

2-D Graphics
3-D Graphics
3-D Animation
Graphical User Interfaces
Plots, Graphs, and Visualization
Games
Audio and Music
Coming Up
Things to Do

Well, art is art, isn’t it? Still, on the other hand, water is water! And east is east and west
is west, and if you take cranberries and stew them like applesauce, they taste much
more like prunes than rhubarb does.
—Groucho Marx

This chapter and the next two discuss the application of Python to some common

human endeavors: art, business, and science. If you’re interested in any of these areas,

you may get some helpful ideas or the urge to try something new.

2-D Graphics

All computer languages have been applied to computer graphics to some degree.

Many of the heavy-duty platforms in this chapter were written in C or C++ for speed,

but added Python libraries for productivity. Let’s begin by looking at some 2-D imag‐

ing libraries.

Standard Library

Only a few image-related modules are in the standard library:

imghdr

Detects the file type of some image files.

colorsys

Converts colors between various systems: RGB, YIQ, HSV, and HLS.

453

If you downloaded the O’Reilly logo to a local file called oreilly.png, you could run

this:

>>> import imghdr
>>> imghdr.what('oreilly.png')
'png'

Another standard library is turtle—“Turtle graphics,” which is sometimes used to

teach programming to young people. You can run a demo with this command:

$ python -m turtledemo

Figure 20-1 shows a screenshot of its rosette example.

Figure 20-1. Image from turtledemo

To do anything serious with graphics in Python, we need to get some third-party

packages. Let’s see what’s out there.

PIL and Pillow

For many years, the Python Image Library (PIL), although not in the standard library,

has been Python’s best-known 2-D image processing library. It predated installers

such as pip, so a “friendly fork” called Pillow was created. Pillow’s imaging code is

backward-compatible with PIL, and its documentation is good, so let’s use it here.

Installation is simple; just type the following command:

$ pip install Pillow

If you’ve already installed operating system packages such as libjpeg, libfreetype,

and zlib, they’ll be detected and used by Pillow. See the installation page for details

on this.

Open an image file:

>>> from PIL import Image
>>> img = Image.open('oreilly.png')
>>> img.format
'PNG'
>>> img.size
(154, 141)
>>> img.mode
'RGB'

Although the package is called Pillow, you import it as PIL to make it compatible

with the older PIL.

To display the image on your screen using the Image object’s show() method, you’ll

first need to install the ImageMagick package described in the next section, and then

try this:

>>> img.show()

The image displayed in Figure 20-2 opens in another window. (This screenshot was

captured on a Mac, where the show() function used the Preview application. Your

window’s appearance might vary.)

Figure 20-2. Image displayed with the Python Image Library

Let’s crop the image in memory, save the result as a new object called img2, and dis‐

play it. Images are always measured by horizontal (x) values and vertical (y) values,

with one corner of the image known as the origin and arbitrarily assigned an x and y

of 0. In this library, the origin (0, 0) is at the upper left of the image, x increases to the

2-D Graphics | 455

right, and y increases as you move down. We want to give the values of left x (55), top

y (70), right x (85), and bottom y (100) to the crop() method, so pass it a tuple with

those values in that order:

>>> crop = (55, 70, 85, 100)
>>> img2 = img.crop(crop)
>>> img2.show()

The results are shown in Figure 20-3.

Figure 20-3. The cropped image

Save an image file with the save method. It takes a filename and an optional type. If

the filename has a suffix, the library uses that to determine the type. But you can also

specify the type explicitly. To save our cropped image as a GIF file, do the following:

>>> img2.save('cropped.gif', 'GIF')
>>> img3 = Image.open('cropped.gif')
>>> img3.format
'GIF'
>>> img3.size
(30, 30)

For our last example, let’s “improve” our little mascot. First download copies of our

original critter, shown in Figure 20-4.

Figure 20-4. Beloved ur-critter

He has a sort of scruffy five o’clock shadow, so let’s get an image to improve his, um,

image; see Figure 20-5.

Figure 20-5. Alien technology

Let’s put them together, with some alpha channel magic to make the overlap semi-

transparent, demonstrated in Example 20-1.

Example 20-1. ch20_critter.py

from PIL import Image

critter = Image.open(‘ch20_critter.png’) stache = Image.open(‘ch20_stache.png’) stache.putalpha(100) img = Image.new(‘RGBA’, critter.size, (255, 255, 255, 0)) img.paste(critter, (0, 0)) img.paste(stache, (45, 90), mask=stache) img.show()

Figure 20-6 presents his makeover.

Figure 20-6. Our new, dapper mascot

ImageMagick

ImageMagick is a suite of programs to convert, modify, and display 2-D bitmap

images. It’s been around for more than 20 years. Various Python libraries have con‐

2-D Graphics | 457

nected to the ImageMagick C library. A recent one that supports Python 3 is wand.

To install it, type the following command:

$ pip install Wand

You can do many of the same things with wand as you can with Pillow:

>>> from wand.image import Image
>>> from wand.display import display
>>>
>>> img = Image(filename='oreilly.png')
>>> img.size
(154, 141)
>>> img.format
'PNG'

As with Pillow, this displays the image on the screen:

>>> display(img)

wand includes rotation, resizing, text and line drawing, format conversion, and other

features that you can also find in Pillow. Both have good APIs and documentation.

3-D Graphics

Some basic Python packages include the following:

VPython has examples that can run in your browser.
pi3d runs on the Raspberry Pi, Windows, Linux, and Android.
Open3D is a full-featured 3-D library.

3-D Animation

Watch the long end-credits for almost any contemporary movie, and you’ll see mass

quantities of people doing special effects and animation. Most of the big studios—

Walt Disney Animation, ILM, Weta, Dreamworks, Pixar—hire people with Python

experience. Do a web search for “python animation jobs” to see what’s available now.

Some Python 3-D packages are:

Panda3D

It’s open source and free to use, even for commercial applications. You can down‐
load a version from the Panda3D website.

VPython

Comes with many examples.

Blender

Blender is a free 3-D animation and game creator. When you download and
install it, it comes bundled with its own copy of Python 3.

Maya

This is a commercial 3-D animation and graphic system. It also comes bundled
with a version of Python, currently 2.7. Chad Vernon has written a free down‐
loadable book, Python Scripting for Maya Artists. If you search for Python and
Maya on the web, you’ll find many other resources, both free and commercial,
including videos.

Houdini

Houdini is commercial, although you can download a free version called
Apprentice. Like the other animation packages, it comes with a Python binding.

Graphical User Interfaces

The name includes the word graphic, but graphical user interfaces (GUIs) concen‐

trate more on the user interface: widgets to present data, input methods, menus, but‐

tons, and windows to frame everything.

The GUI programming wiki page and FAQ list many Python-powered GUIs. Let’s

begin with the only one that’s built in to the standard library: Tkinter. It’s plain, but it

works on all platforms to produce native-looking windows and widgets.

Here’s a teeny, tiny Tkinter program to display our favorite googly-eyed mascot in a

window:

>>> import tkinter
>>> from PIL import Image, ImageTk
>>>
>>> main = tkinter.Tk()
>>> img = Image.open('oreilly.png')
>>> tkimg = ImageTk.PhotoImage(img)
>>> tkinter.Label(main, image=tkimg).pack()
>>> main.mainloop()

Notice that it used some modules from PIL/Pillow. You should see the O’Reilly logo

again, as shown in Figure 20-7.

Graphical User Interfaces | 459

Figure 20-7. Image displayed with Tkinter

To make the window go away, click its close button, or leave your Python interpreter.

You can read more about Tkinter at the tkinter wiki. Now for the GUIs that are not in

the standard library:

This is a professional GUI and application toolkit, originated about 20 years ago
by Trolltech in Norway. It’s been used to help build applications such as Google
Earth, Maya, and Skype. It was also used as the base for KDE, a Linux desktop.
There are two main Python libraries for Qt: PySide is free (LGPL license), and
PyQt is licensed either with the GPL or commercially. The Qt folks see these dif‐
ferences. Download PySide from PyPI or Qt and read the tutorial. You can
download Qt for free online.

GTK+

GTK+ is a competitor of Qt, and it, too, has been used to create many applica‐
tions, including GIMP and the Gnome desktop for Linux. The Python binding is
PyGTK. To download the code, go to the PyGTK site, where you can also read
the documents.

WxPython

This is the Python binding for WxWidgets. It’s another hefty package, free to
download online.

Kivy

Kivy is a free modern library for building multimedia user interfaces portably
across platforms—desktop (Windows, macOS, Linux), and mobile (Android,
iOS). It includes multitouch support. You can download for all the platforms on
the Kivy website. Kivy includes application development tutorials.

PySimpleGUI

Write native or web-based GUIs with one library. PySimpleGUI is a wrapper for
some of the other GUIs mentioned in this section, including Tk, Kivy, and Qt.

The web

Frameworks such as Qt use native components, but some others use the web.
After all, the web is a universal GUI, and it has graphics (SVG), text (HTML),
and even multimedia now (in HTML5). You can build web applications with any
combination of frontend (browser-based) and backend (web server) tools. A thin
client lets the backend do most of the work. If the frontend dominates, it’s a thick,
or fat, or rich client; the last adjective sounds more flattering. It’s common for the
sides to communicate with RESTful APIs, Ajax, and JSON.

Plots, Graphs, and Visualization

Python has become a leading solution for plots, graphs, and data visualization. It’s

especially popular in science, which is covered in Chapter 22. Useful overviews, with

examples, include the official Python wiki and the Python Graph Gallery.

Let’s look at the most popular ones. In the next chapter, you’ll see some of these again,

but being used to create maps.

Matplotlib

The Matplotlib 2-D plotting library can be installed by using the following command:

$ pip install matplotlib

The examples in the gallery show the breadth of Matplotlib.

Let’s first try the same image display application (with results shown in Figure 20-8),

just to see how the code and presentation look:

import matplotlib.pyplot as plot
import matplotlib.image as image

img = image.imread('oreilly.png')
plot.imshow(img)
plot.show()

Plots, Graphs, and Visualization | 461

Figure 20-8. Image displayed with Matplotlib

The real strength of Matplotlib is in plotting, which is, after all, its middle name. Let’s

generate two lists of 20 integers, one smoothly increasing from 1 to 20, and another

like the first, but with slight wobbles now and then (Example 20-2).

Example 20-2. ch20_matplotlib.py

import matplotlib.pyplot as plt from random import randint

linear = list(range(1, 21)) wiggly = list(num + randint(-1, 1) for num in linear)

fig, plots = plt.subplots(nrows=1, ncols=3)

ticks = list(range(0, 21, 5)) for plot in plots: plot.set_xticks(ticks) plot.set_yticks(ticks)

plots[0].scatter(linear, wiggly)

plots[1].plot(linear, wiggly) plots[2].plot(linear, wiggly, ‘o-‘)

plt.show()

If you run this program, you’ll see something like what’s shown in Figure 20-9 (not

exactly, because the randint() calls make random wiggles).

Figure 20-9. Basic Matplotlib scatter and line plots

This example showed a scatterplot, a line plot, and a line plot with data markers. All

of the styles and colors used Matplotlib defaults, but they can be customized very

extensively. For details, see the Matplotlib site or an overview like Python Plotting

With Matplotlib (Guide).

You can see more of Matplotlib in Chapter 22; it has strong ties to NumPy and other

scientific applications.

Plots, Graphs, and Visualization | 463

Seaborn

Seaborn is a data visualization library (Figure 20-10), built on Matplotlib and with

connections to Pandas. The usual installation mantra (pip install seaborn) works.

Figure 20-10. Basic Seaborn scatter plot and linear regression

The code in Example 20-3 is based on a Seaborn example; it accesses test data on res‐

taurant tipping and plots tips versus total bill amounts with a fitted linear regression

line.

Example 20-3. ch20_seaborn.py

import seaborn as sns import matplotlib.pyplot as plt

tips = sns.load_dataset(“tips”) sns.regplot(x=”total_bill”, y=”tip”, data=tips);

plt.show()

If you run the preceding code with the standard Python interpreter,
you need that initial import line (import matplotlib.pyplot as
plt) and final line (plt.show()), as shown in Example 20-3, or else
the plot just won’t display. If you’re using Jupyter, Matplotlib is built
in and you don’t need to type them. Remember this when you read
code examples of Python mapping tools.

Like Matplotlib, Seaborn has a vast number of options for data handling and display.

Bokeh

In the old web days, developers would generate graphics on the server and give the

web browser some URL to access them. More recently, JavaScript has gained perfor‐

mance and client-side graphics generation tools like D3. A page or two ago, I men‐

tioned the possibility of using Python as part of a frontend-backend architecture for

graphics and GUIs. A new tool called Bokeh combines the strengths of Python (large

data sets, ease of use) and JavaScript (interactivity, less graphics latency). Its emphasis

is quick visualization of large data sets.

If you’ve already installed its prerequisites (NumPy, Pandas, and Redis), you can

install Bokeh by typing this command:

$ pip install bokeh

(You can see NumPy and Pandas in action in Chapter 22.)

Or, install everything at once from the Bokeh website. Although Matplotlib runs on

the server, Bokeh runs mainly in the browser and can take advantage of recent advan‐

ces on the client side. Click any image in the gallery for an interactive view of the dis‐

play and its Python code.

Games

Python is such a good game development platform that people have written books

about it:

Invent Your Own Computer Games with Python by Al Sweigart
The Python Game Book by Horst Jens (a docuwiki book)

There’s a general discussion at the Python wiki with even more links.

The best known Python game platform is probably pygame. You can download an

executable installer for your platform from the Pygame website, and read a line-by-

line example of a “pummel the chimp” game.

Games | 465

Audio and Music

I sought the serif
But that did not suit Claude Debussy.
—Deservedly Anonymous

What about sound, and music, and cats singing “Jingle Bells”? Well, as Meatloaf says,

two out of three ain’t bad.

It’s hard to represent sound in a printed book, so here are some up-to-date links to

Python packages for sound and music, but Google has many more:

Standard library audio modules
Third-party audio tools
Dozens of third-party music applications: graphic and CLI players, converters, notation, analysis, playlists, MIDI, and more

Finally, how about some online sources of music? You’ve seen code examples

throughout this book that access the Internet Archive. Here are links to some of its

audio archives:

Audio recordings (>5 million)
Live music (>200,000)
Live Grateful Dead shows (>13,000)

Coming Up

Act busy! It’s Python in business.

Things to Do

20.1 Install matplotlib. Draw a scatter diagram of these (x, y) pairs: ( (0, 0), (3,

5), (6, 2), (9, 8), (14, 10) ).

20.2 Draw a line graph of the same data.

20.3 Draw a plot (a line graph with markers) of the same data.