What do you find most readable: your version, with an ad-hoc function defined somewhere else, far away in the code, or a simpler: for (x,y,z=0) in tupleList: do_whatever_with_it()
I came up with the "ad-hoc function" to give a kind of replacement for the used syntax, in order not to ask why not immediately: for tuple in tupleList: do_whatever_with_it() ?
What if do_whatever_with_it() waits for a triplet, we have a list of mixed pairs and triplets, and augmenting pairs with a 0 would do for us?
As I said, there's always a way to do it as long as the language is turing complete. The problem is with is of use and readiblity - expressive power - which, I agree, is at least somewhat subjective !-)
Sure I like the syntax as long as I think in terms of unpacking tuples, but at the first glance I thought that the intention was to get only x, y from the tuple setting all z in the yielded tuples to zero (as suggested in this thread by giving the example of going from 3D down to 2D where with all z=0 the algorithm will remain the same). What about "for (x,y,if z not in tupleList: z=0 else: z=1) in tupleList" ?
Should be: for x, y, if [???]:z=0 else:z=1 in tupleList: # etc
This Would do for me. But since we're not going to have a ternary woperator (or everything's-an-expression for that matter)...
What if the tupleList is empty?
No iteration.
Should existing z be set to zero or not after the line with the for loop was executed?
should follow the same rule as for other vars.
Should for (,y) in tupleList: do_whatever_with_it() give only the y and for (,,z) in tupleList: only the z values?
Don't know. Didn't think of it.
If it should become possible to use the "for (x,y,z=0) in tupleList" syntax, I would sure like also to have: "for (,,z) in tupleList"
Sounds coherent... but then you already have: for dont_care, ignore, y in tupleList: # etc
"for (x,y,if z not in tupleList: z=0 else: z=1) in tupleList" "for (x,y,if z not in tupleList: z=0 else: z=2*x*z) in tupleList" and sure also: "for (x,y,z=0, *r) in tupleList" etc.
My only objections are:
Is it worth the effort? Would it not be confusing?
Maybe starting with e.g. a xlistcomprehension module where xlistcomprehension.execute( "[for (x,y,if z not in tupleList: z=0 else: z=1) in tupleList]" ) or just xl(...) to keep it short provides the desired functionality is a good idea? Then it can be seen if this module becomes widely used and therefore worth to be integrated?
I don't think this would be possible. What is proposed requires modification to the language itself AFAICT.
I think it would be nice to have, but I can't imagine it to be really very helpful.
I once had the same feeling about first class functions, higher-order functions, lambdas, list comprehension, __call__ special method, descriptors, metaclasses, and a whole lot of other constructs for that matter. Now I woul be very unhappy not to have them !-)
Regards,
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bruno desthuilliers
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