The Scientist & The Engineer

Transcript

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   THE SCIENTIST ANDREW GODWIN // @andrewgodwin THE ENGINEER AND

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   Hi, I’m Andrew Godwin

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   I call myself an "engineer"

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   But I studied Computer Science

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   I knew programming going in. But this was different.

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   “ Edsger Dijkstra Computer science is no more about computers

   than astronomy is about telescopes.
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   Computer Science is idealistic

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   "Turing-complete"

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   We first want to prove it is possible

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    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
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    We can prove that programs are correct

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    def is_two(number): return number == 2

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    >>> import __builtin__ >>> __builtin__.True = False >>> True False

    >>> True == False True (Thankfully, only works in Python 2!)
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    "Communicating Sequential Processes", C. A. R Hoare

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    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
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    A perfect world, of perfect programs

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    “ Benjamin Brewster In theory there is no difference between

    theory and practice. In practice there is.
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    Software Engineering takes shortcuts

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    When is it safe to take a risk?

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    None
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    Software is faster and cheaper to change

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    The real world is a nasty place

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    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!
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    Always design for failure

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    How do we reason about software?

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    Input Process Output

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    async def disable_alarm(): ... async def open_door(): ... await asyncio.wait(

    [disable_alarm(), open_door()] )
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    Input Rendering Output Validation Reporting Storage Processing Logging Cache

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    Django has 250,000 lines of code

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    An Airbus A380 has 4,000,000 parts

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    A new car has 100,000,000 lines of code

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    How are we supposed to handle this?

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    Abstract, verify and forget

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    Abstract Define a contract - types, behaviour, exceptions Verify Write

    tests to keep the contract valid Forget Work with the contract, not the fine details
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    You have to learn to forget

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    Engineering is communication

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    “ Grace Hopper A ship in port is safe, but

    that's not what ships are built for.
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    Build to expect growth

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    Build to expect failure

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    Everyone can build near-perfect software

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    Know when not to!

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    Python lets you do both.

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    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.
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    Scientists observe and question

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    Engineers build and invent

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    All software has consequences

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    Be the scientist and the engineer

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    Gracias. Andrew Godwin @andrewgodwin // aeracode.org