On Thu, Mar 1, 2018 at 8:38 AM, Robert Vanden Eynde <robertve92@gmail.com> wrote:
Le 28 févr. 2018 11:43, "Chris Angelico" <rosuav@gmail.com> a écrit :
If you aren't using the variable multiple times, there's no point giving it a name. Unless I'm missing something here?
Yes, variables are not there "just because we reuse them", but also to include temporary variables to better understand the code. Same for functions, you could inline functions when used only once, but you introduce them for clarity no ?
Sure, but if you're creating temporaries for clarity, you should probably make them regular variables, not statement-local ones. If you're going to use something only once and you don't want to break it out into a separate statement, just use a comment.
``` a = v ** 2 / R # the acceleration in a circular motion f = m * a # law of Newton ```
could be written as
``` f = m * (v ** 2 / R) # compute the force, trivial ```
But having temporary variables help a lot to understand the code, otherwise why would we create temporary variables ? I can give you an example where you do a process and each time the variable is used only one.
Neither of your examples needs SLNBs.
Scoping is a fundamental part of both my proposal and the others I've seen here. (BTW, that would be a NameError, not a SyntaxError; it's perfectly legal to ask for the name 'y', it just hasn't been given any value.) By my definition, the variable is locked to the statement that created it, even if that's a compound statement. By the definition of a "(expr given var = expr)" proposal, it would be locked to that single expression.
Confer the discussion on scoping on github (https://github.com/python/peps/commit/2b4ca20963a24cf5faac054226857ea9705471...) :
""" In the current implementation it looks like it is like a regular assignment (function local then).
Therefore in the expression usage, the usefulness would be debatable (just assign before).
But in a list comprehension after the for (as I mentioned in my mail), aka. when used as a replacement for for y in [ x + 1 ] this would make sense.
But I think that it would be much better to have a local scope, in the parenthesis. So that print(y+2 where y = x + 1) wouldn't leak y. And when there are no parenthesis like in a = y+2 where y = x+1, it would imply one, giving the same effect as a = (y+2 where y = x+1). Moreover, it would naturally shadow variables in the outermost scope.
So the question is: what is the benefit of the local name 'y'? In any non-trivial example, it's not going to fit in a single line, so you have to either wrap it as a single expression (one that's been made larger by the "where" clause at the end), or break it out into a real variable as a separate assignment. ChrisA