1. Core 1b – Engineering Dynamic Coding a.k.a. Python in Slicer
Steve Pieper
Isomics, Inc.

2. Overview The Role of Dynamic Coding
Practical Slicer Python Programming
Python Examples and Resources
Bonus Language

3. Typical Development Workflows
Start Slicer
Load Data
Test Code
Edit Code
Compile
Start Slicer
Load Data
Test Code
Edit Code
Reload
C++
Python

4. Tradeoffs: C++ C++ Advantages C++ Negatives Access to the Compiler
Templates
Iterators
Declared Typing
Efficiency: Pointer Arithmetic / Iterators
Symbolic Debugging
C++ Negatives
Verbosity
Run-Time Rigidity
Errors Often Fatal

5. Tradeoffs: Python Python Advantages Python Negatives
Expressiveness: Less Code == Less Clutter
Run-Time Flexibility
Code Can be Redefined on the Fly
Console Access to Program State
Unified Coding / Testing / Debugging
Python Negatives
Incomplete
Not all C/C++ APIs are Exposed
Not an “Assembler Replacement”
Asymmetric: Less Common to Expose Python APIs to C++
Code Size / Load Time
Heavy Dependencies

6. Language Independent Truisms
Bad Code is Bad Code
Follow Good Design Examples: Qt
Programming Is a Lot of Work
Write Tests & Documentation; Support Your Code
Consider Your Job, Colleagues, and Users
Write Maintainable, Reusable Code
Provide a Clean Interface (Ideally Pure Data - MRML)
Don’t Sacrifice the User’s Interests for the Sake of Language Purity
Try to Pick the Right Tool for the Job
If There’s a Great Library, Use It.
Always Consider the License
Good: BSD, Apache 2.0, LGPL
Bad: GPL, Proprietary, “Free for Academic”, Closed Source

7. Python Interaction Example
b = qt.QPushButton('Toggle')
b.connect('clicked()', toggle)
b.show()

8. What’s Available in Python?
Basically Everything
VTK Pipelines
Qt Interfaces via PythonQt
SimpleITK (Work in Progress)
MRML, Slicer Logic, Slicer GUI
Modules Logics, CLIs
But there are Limits
Slicer Ships with Python 2.6 (not 2.7 or 3.x)
Some Popular Python Libraries NOT Available in Distribution
Scipy, matplotlib, iPython, PyOpenCL…
Some Open Design Tradeoffs
Reasonable People can Disagree on Best Implementation Choice for Any Given Task

9. Structure of a Scripted Module
Logic
Structure as a ‘Python Module’ for Import in Other ‘Slicer Modules’
No GUI Dependencies
No QtGui or vtkRendering classes
Widget
Implements the Slicer Module GUI
Package Components Reusable in Other Modules (Editor)
Self Test
Essential Component of Your Development Workflow
Runable by End User on Their Installation
Automatically a CTest

10. Examples and Resources
DICOM Module
Editor Module
Editor Extensions
DataProbe, LabelStatistics, Endoscopy…
Diffusion Processing Wizard
PET/CT Extension
Self Tests
RSNA 2012
Atlas Tests
Python Programming Tutorial at slicer.org

11. Bonus Language: JavaScript!
Arguably the Most Popular Language in 2012 (google it)
You Probably Spend a Good Portion of Your Day Running JavaScript (GMail, github, …)
JavaScript is a Great Language (XTK…)
Qt (and therefore Slicer) Includes a Full WebKit Engine
Like in Chrome and Safari
HTML5/CSS/JavaScript: World Class Look & Feel
Better WebKit in Qt5, Coming Soon (WebGL, …)
Great JavaScript Libraries Work in Slicer
jQuery, jQueryUI, d3js…
Slicer 4.2 Usage in Slicer
qMRMLChartView Implemented with jQPlot
Extension Manager is a qWebView
Remember the Programming Truisms…