All entries for Thursday 10 October 2019

October 10, 2019

The Basics aren't so Basic

Sorry for the long break! We've been busy with the start of term and busy expanding our training material (link). This week I am just going to talk about something that you should always keep in mind, not just with programming and computers but with a whole bunch of things, and that is, what does it mean to say something is "basic".

There is a quote often attributed to Einstein, although not directly traceable to himwhich goes

Common sense is the collection of prejudices acquired by age eighteen.

Whether the origin is real or not, it's often true that what people think is simple, or "just common sense" is only so because of their background. To somebody who cut teeth on a BBC Micro, programming might seem super BASIC.

Jokes aside, you will probably keep coming across things that are super-basic and feeling a bit awkward that they somehow escaped you until now. Especially if you have learned things in the usual manner, i.e. by necessity, it is very easy to miss some of the basics. You can find yourself doing really quite advanced things, while not knowing something that "everybody else" seems to. This is normal. It is not beneficial, but it is perfectly normal. Frankly, in computing and programming there is a vast, vast sea of "basics", and no matter how much you learn there always seems to be more.

When I were a Lad

When I was a PhD student, I was happily using 'ssh' to login to remote machines, but I would always type out the whole host spec, such as "username@machinename.blah". I remember feeling a bit dumb when my supervisor pointed out that I didn't need the "username", and he thought this was somehow basic and obvious. I was frankly a little bit irritated because nobody told me! How was I meant to know?

"Simplicity is the final achievement."

(Quote from Frederic Chopin)

Moreover, just because something is "basic" doesn't mean it is simple. In fact, Merriam-Webster's definitionof the adjective "basic", while perhaps a bit unhelpfully recursive does not say simple anywhere. That thing with the username isn't so simple. It's fundamental, sure, but it's not simple!

Years later, I am still regularly coming across things that are "basic" that I have never encountered before. The whole "learning how to program" thing is far more of a helix than a road. You come across fundamental things all the time, some for the first time, some repeatedly, and often you can understand them better every time. Eventually, you find them simple. Sometimes they feel even elegant, because they arise so smoothly from the things you do know, or perhaps even seem so obviously "the only way it could be".

This is most of the motivation for our "WINKT" blog post series. These are fundamental, mostly "basic" things, but they're mostly not things you could usefully be told about the first go-around. Mostly, they are the basics of how the complicated things work. For example:

  • On the command line: if you use the '*' wildcard, when does this get expanded into the list of matches? Specifically, if you accidentally create a file called "-rf" in your home, and ran the command `rm *` to remove files, how much trouble would you be in? The answer is, _a lot_. * is processed first, by the shell, and unfortunately '-' comes first in the alphabet. You just ran the equivalent of `rm -rf *`. Ooops.

  • Any C/C++ programmers: if you use a variable which is undefined, what is it's value? If you said "whatever is in the associated memory beforehand", you're close, but wrong. An undefined variable is undefined behaviour - it can be given any value, including a different one each time it is accessed. Why? Because the standard says so. But who needs to know that? It is enough to know that its value is unreliable. Using your "basic" knowledge of the C memory model, you would likely guess the above, and it would never matter. [Disclaimer: this is one that I personally only learned a few weeks ago. It's absolutely fundamental, but not at all simple.]

  • For Fortran 2003 people: if you have a function-scoped ALLOCATABLE array, allocate it inside the function and forget to free it before the function exits, what happens? A memory leak? Nope! Fortran will helpfully deallocate the array on exit. If you didn't know this and freed everything yourself, there would never be a problem, but this one often surprises people.

  • For Python people: suppose you give a function a default argument, like `def func(arg, list_arg = []): ...` and suppose inside the function, list_arg gets filled with stuff. If you call the function twice without supplying list_arg, what do you get the second time? If you said "the combined contents from the first and second calls" you would be correct! The default arg. is an empty list, but it is the SAME empty list each time!

Take Aways

What's the point of all this rambling? Just that there is so much often classed as "the basics" that nobodycan know it all, and there is nothing so basic that you wouldn't do well to re-examine it anyway. It gets said all the time, but with computers there really are no stupid questions. Well, OK, there are some pretty stupid questions. But I have never seen one yet that wasn't worth thinking about.

Postscript: any suggestions for things that make you go "Well I Never Knew That"!, email us or comment! We can always use more

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