Python Error Handling

Part I: Famous Software Failures

Therac-25 (1985-1987)

Computer-controlled radiation therapy machine

The Problem:

• Machine could produce:
  1. Low-energy electron beams
  2. High-energy X-ray photons
• A turntable must be set up correctly for each mode
• Race condition allowed high-powered beams when turntable was NOT in correct position
• Result: Massively overdosed 6 people; several died

Lesson: Proper error handling and testing of control systems is critical

Ariane 5 Rocket (1996)

The Incident:

• Normal behavior for 36s after lift-off
• Failure of both Inertial Reference Systems simultaneously
• Strong pivoting of nozzles → 90 degree off-course
• Self-destruction at 4000m altitude
• Cost: $7 billion development + $500 million rocket/cargo

What Went Wrong:

• Overflow on one variable representing horizontal velocity