for x,y,z in some_iterator:
If some_iterator produces at some time a tuple with only two elements this will raise an exception no matter whether you assigned z already or not.
So if I now understand it right, the core of the whole proposal is to find a way to make unpacking of tuples work also in case the tuples have not the appropriate number of elements, right?
That's the original problem at least. Kay seems to be wanting to extend a possible solution to this problem to a lambda replacement, which is IMHO another point.
So to achieve the same effect I need currently (not tested):
for x,y,z in [getMyTargetTupleFrom(currentTuple) for currentTuple in tupleList]
where getMyTargetTupleFrom(currentTuple) is:
def getMyTargetTupleFrom(currentTuple): if len(currentTuple) >= 3: return (currentTuple[0], currentTuple[1], currentTuple[2]) if len(currentTuple) == 2: return (currentTuple[0], currentTuple[1], 0)
right?
Yes
Is it really worth it?
I think so. The problem of "unpacking tuple of the wrong size" is a common one (at least for me), and having to write a special function to handle the case, or use try:except blocks, dont make for more readable code IMHO. The possibility to clearly and cleanly handle the case *when it's an expected case* and *as close as possible* to where it happens would (always IMHO) improve readability.
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()
Isn't it much easier to convert the list of tuples explicit to appropriate format, first?
This *is* an explicit conversion. Much more explicit than a function buried xxx lines of code away IMHO. (and BTW, It also avoid to have to build two lists.)
It seems, that my attitude to the proposal is originated from bad experience with default values.
To get it tracked down to the point:
In my opinion default values are evil and it is enough trouble that function defintions allow them.
Python would barely be usable without.
I have seen already postings of confused newbies expecting the default values beeing set during function execution not during definition and I have also faced this problem starting on Python myself .
There are a lot of features in any language that are at first sight confusing, specially when these features look like features existing in another language but fail to behave like in the other language.
<half-troll>
Removing anything that could confuse anyone having only experience with language X or Y leads to Java - an average language designed for average programmers, where the lack of expressive power leads to overly complicated code to get simple things done.
</half-troll>
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bruno desthuilliers
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