unpaking sequences of unknown length

[Gerard Flanagan]

Anthra Norell wrote:
> Hi,
>
>    I keep working around a little problem with unpacking in cases in which I don't know how many elements I get. Consider this:
>
>       def  tabulate_lists (*arbitray_number_of_lists):
>             table = zip (arbitray_number_of_lists)
>             for record in table:
>                # etc ...
>
> This does not work, because the zip function also has an *arg parameter, which expects an arbitrary length enumeration of arguments

maybe I don't understand the problem properly, but you can use '*args'
as 'args' or as '*args', if you see what I mean!, ie.

       def  tabulate_lists (*arbitray_number_of_lists):
             table = zip (*arbitray_number_of_lists)
             for record in table:
                # etc ...

for example:

def sum_columns(*rows):
    for col in zip(*rows):
        yield sum(col)

for i, s in enumerate( sum_columns( [1,2], [3,2], [5,1] ) ):
    print 'Column %s: SUM=%s' % (i,s)

Column 0: SUM=9
Column 1: SUM=5

-----------------------------------------------------

alternatively:

import itertools as it

def sum_columns2( iterable ):
    for col in it.izip( *iterable ):
        yield sum(col)

def iter_rows():
    yield [1,2]
    yield [3,2]
    yield [5,1]

print list(  sum_columns2( iter_rows() ) )

#(izip isn't necessary here, zip would do.)

-----------------------------------

Gerard