Teaching Python with Graphics

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Teaching Python with Graphics

• by Kirby Urner

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The Challenge

• How might we generate interesting graphics
  while learning to program in core Python?

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Pitfalls

• Getting lost in an elaborate API that takes
  attention away from core Python
• Too much code for learning purposes (smallish
  projects required)
• Resulting graphics are trivial and/or
  uninteresting

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Some Solutions

• Wrap the graphics API, or use just a few of an
  applications features
• Recycle code use classes to isolate API-specific
  methods from generic methods
• Look for reusable data in text format and/or use
  simple algorithms that generate complex patterns

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Example Using POV-Ray

• Simplify API edge, point, face
• Gradually build up a generic Vector class
• Sources of polyhedra on the web

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Standard Core Python
def getedges (faces) """ Return unique
edges from a list of faces -- edges(f) for
rotate/zip) """ alledges sets.Set()
for f in faces for p in edges( f )
e list( p ) e.sort( )
alledges.add( tuple(e) ) return list(alledges)
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A POV-Ray Writer
class Povray (object) """Skeletal outline of a
POV-Ray writer object" " " def __init__
(self, filename) self.output
file(filename, 'w') self.header() def
header (self) pass def edge (self, v0, v1)
pass def face (self, vlist) pass def
point (self, v0) pass def close (self)
self.output.close()
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Vector Module

• How much detail depends on mathematical needs,
  interests, goals of student
• Prime example of where operator overloading makes
  so much sense
• Easy to play with interactively (in shell), even
  if the code is pre-written (many examples of
  vectors.py out there)

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Python is Interactive!
gtgtgt v0 Vector3d(1,1,0) gtgtgt v0 Vector (1, 1,
0) gtgtgt v0.rotate(90,axis'x') Vector (1.0,
2.22044604925e-016, 1.0) gtgtgt v0.rotate(90,axis'y
') Vector (2.22044604925e-016, 1.0, -1.0) gtgtgt
v0.spherical() (1.4142135600000001, 90.0,
45.0) gtgtgt v0.rotate(90,axis'y').spherical() (1.4
142135600000001, 135.0, 90.0)
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Final Puzzle Piece A Shape Class
class Shape def __init__ (self, faces,
points) def translate (self, v) def
rotate (self, degrees, axis) def getcenter
(self) def center (self) def
scale (self, factor) def
__repr__ (self) def display (self, output)
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Core Python Topics Explored

• Edges from Faces data structures, import
• String substitution POV-Ray methods
• Classes POV-Ray writer, Shape
• Operator Overloading Vector class
• File I/O parsing input, writing output

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Summay of PIL example

• Focus is on mathematics PIL does not get in the
  way
• Core algorithm is simple, result is complex
• Python may clarify mathematical relationships
  (Mandelbrot as subclass of Julia)

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gtgtgt rule nks.makerule(30) wolfram numbering
scheme a useful Python exercise gtgtgt
nks.sayrule(rule) 111 --gt 0 110 --gt 0 101 --gt
0 100 --gt 1 011 --gt 1 010 --gt 1 001 --gt 1 000 --gt
0
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Motion Three Demonstrations

• Python POV-Ray with a built-in clock
  generates animations, including mpeg clips
• VPython provides an API to OpenGL for real time
  experience (similar to VRML) PyGeo an example
  of an app that wraps VPython
• PyGame provides an API to 2D sprites, with
  collision detection and sound

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Thank You

• ContactKirby Urner kirby_at_4dsolutions.net
• These slides and source codehttp//www.4dsolutio
  ns.net/oscon2004/(and via the official OSCON
  site)

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