[Tutor] small problem with lists/tuples

[Gregor Lingl]

Thomi Richards schrieb:

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>Hi all,
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>...
>

>['data']
>
>or:
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>[['data']]
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>or even:
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>([['data']])
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>what I'm trying to do, is "unpack" the duples, until i get to the actual data 
>inside. Originally, i thought I could do it something like this:
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>  
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Sometimes you will encounter the problem to get to the "actual data", 
when they are packed in
some more complicated ("nested") lists or tuples, e.g.:
([1],[[2]],[[3,[[[4]]],[5]]])  ==> [1,2,3,4,5]

This can be accomplished by "flattening" these nested lists:

 >>> def flatten(seq):
        flat = []
        for item in seq:  # simple member
                if not (isinstance(item,list) or isinstance(item,tuple)):
                        flat.append(item)
                else:     # sequence, so flatten this one too
                        flat.extend(flatten(item))
        return flat  # or if you want: return tuple(flat)

 >>> flatten((1,(2,3)))
[1, 2, 3]
 >>> flatten(([1],[[2]],[[3,[[[4]]],[5]]]))
[1, 2, 3, 4, 5]
 >>> flatten([0,[1],[[2]],[[3,[([4],)],[5]]],("wow",)])
[0, 1, 2, 3, 4, 5, 'wow']

With flatten you can easily define a getdata like you need it:

 >>> def getdata(data):
        return flatten(data)[0]

 >>> print data1, getdata(data1)
['data'] data
 >>> print data2, getdata(data2)
[['data']] data
 >>> print data3, getdata(data3)
([['data']],) data
 >>> print data, getdata(data)
([['d']],) d
 >>>

Regards, Gregor