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The Scientist & The Engineer
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Andrew Godwin
February 07, 2020
Programming
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The Scientist & The Engineer
My keynote from PyCon Colombia 2020.
Andrew Godwin
February 07, 2020
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Transcript
THE SCIENTIST ANDREW GODWIN // @andrewgodwin THE ENGINEER AND
Hi, I’m Andrew Godwin
I call myself an "engineer"
But I studied Computer Science
I knew programming going in. But this was different.
“ Edsger Dijkstra Computer science is no more about computers
than astronomy is about telescopes.
Computer Science is idealistic
"Turing-complete"
We first want to prove it is possible
async def sleep_sort(numbers): async def sleep_add(number): await asyncio.sleep(number) result.append(number) result
= [] await asyncio.wait([ sleep_add(number) for number in numbers ]) return result
We can prove that programs are correct
def is_two(number): return number == 2
>>> import __builtin__ >>> __builtin__.True = False >>> True False
>>> True == False True (Thankfully, only works in Python 2!)
"Communicating Sequential Processes", C. A. R Hoare
contains :: (Ord a) => (Tree a) -> a ->
Bool contains Nil _ = False contains (Node t1 v t2) x | x == v = True | x < v = contains t1 x | x > v = contains t2 x
A perfect world, of perfect programs
“ Benjamin Brewster In theory there is no difference between
theory and practice. In practice there is.
Software Engineering takes shortcuts
When is it safe to take a risk?
None
Software is faster and cheaper to change
The real world is a nasty place
How often does a cosmic ray affect RAM? 36 hours
(for 16GB; "SEU at Ground Level", Eugene Normand) How long can an unpowered SSD keep data? 3 weeks - 1 year (Enterprise at 40ºC, Client at 30ºC; Intel/JEDEC) Does quantum tunneling affect CPUs? Continuously!
Always design for failure
How do we reason about software?
Input Process Output
async def disable_alarm(): ... async def open_door(): ... await asyncio.wait(
[disable_alarm(), open_door()] )
Input Rendering Output Validation Reporting Storage Processing Logging Cache
Django has 250,000 lines of code
An Airbus A380 has 4,000,000 parts
A new car has 100,000,000 lines of code
How are we supposed to handle this?
Abstract, verify and forget
Abstract Define a contract - types, behaviour, exceptions Verify Write
tests to keep the contract valid Forget Work with the contract, not the fine details
You have to learn to forget
Engineering is communication
“ Grace Hopper A ship in port is safe, but
that's not what ships are built for.
Build to expect growth
Build to expect failure
Everyone can build near-perfect software
Know when not to!
Python lets you do both.
Types Start without types, progressively add with mypy Async Make
it work synchronously first. Add async later. Speed Write slow, understandable code. Test it. Then improve it.
Scientists observe and question
Engineers build and invent
All software has consequences
Be the scientist and the engineer
Gracias. Andrew Godwin @andrewgodwin // aeracode.org