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Comment by tikhonj | Hacker News Reader

Trailing commas are really easy to miss. When reading this line of code, I did not notice it immediately; I originally assumed that varname was being assigned a list.

This sort of code would be very confusing when I'm just quickly reading through a procedure trying to find the potential bug.

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Indeed. I prefer the following variant which is more explicit and thus (IMHO) more in the spirit of Python:

   (varname,) = [x for x in l if predicate_with_single_truth_value(x)]

Agreed. It could be written much more clearly in my opinion like this:

    [varname] = [x for x in l if predicate_with_single_truth_value(x)]

I had to check that on the REPL. I'm surprised that even works and I can't think of a good reason why should list syntax be allowed as a lvalue, in addition to tuple syntax.

It's called destructuring assignment. It's been around for a while.

http://dunsmor.com/lisp/onlisp/onlisp_22.html

I mean why would you want to allow both list and tuple syntax for exactly the same semantics, when either of them would be enough.

I just wish we had destructing assignment for other types as well. And maybe a proper pattern matching!

Good idea!

You could also use the ,= operator, of course:

varname ,= [...]

It appears to me that there is actually no such operator in Python; cf. http://docs.python.org/reference/simple_stmts.html#augmented...

Superficially it looks like an operator, but I suspect that's merely because of whitespace freedom; i.e., a, = [0] is equivalent to a,=[0] and a ,= [0].

I assume it was a joke; a pop culture reference to this stack overflow question:

http://stackoverflow.com/questions/1642028/what-is-the-name-...

  Sure it is! And in Python 3 there's the ,_*= operator, similar to lisp's car:

  varname ,_*= [1, 2, 3] # varname == 1

HN isn't the place for facetiousness.

Apparently it isn't the place for humour either.

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