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pythonlistlist-comprehension

What's an elegant way to extract a series of entries in a list of tuples into sublists?

Say I have a series of entries in a list of tuples like this:

TRUE = 1
listOfTuples = [('selectable', 'frequency'), ('color', 'green'), ('item', '10 Hz'), 
                ('value', 10), ('align', 'left'), ('hidden', TRUE), ('item', '20 Hz'), 
                ('value', 20), ('align', 'right'), ('item', '50 Hz'), ('value', 50), 
                ('item', '100 Hz'), ('value', 100), ('textColor', 0xFF0000)]

Now I want to extract a list with individual item entries like this:

[(('item', '10 Hz'), ('value', 10), ('align', 'left'), ('hidden', TRUE)),
 (('item', '20 Hz'), ('value', 20), ('align', 'right')),
 (('item', '50 Hz'), ('value', 50)), 
 (('item', '100 Hz'), ('value', 100), ('textColor', '0xFF0000'))]

The delimiting keyword to identify a sublist is always item or the end of the list. There can be an arbitrary number of tuples between two adjacent delimiters. The content of the list before the first occurrence of item is to be ignored. The detection of the keyword item should be case insensitive.

I am not a Python afficionado, so I don't know how to apply something like list comprehension (if that's actually possible), given that I need to extract lists between delimiters. Of course I can do it the pedestrian way by traversing through the list, identifying the positions of the keyword in the tuples and then extracting the sublists but I was hoping for a more elegant solution.

Solution

  • You can use tuple() function to transform lists into tuples, so you will be able to append all of the tuples inside listOfTuples variable into the output that you need:

    TRUE = 1
lot = [('selectable', 'frequency'), ('color', 'green'), ('item', '10 Hz'), 
                ('value', 10), ('align', 'left'), ('hidden', TRUE), ('item', '20 Hz'), 
                ('value', 20), ('align', 'right'), ('item', '50 Hz'), ('value', 50), 
                ('item', '100 Hz'), ('value', 100), ('textColor', 0xFF0000)]

l = [[]]
for i in lot:
    if i[0]=='item':
        l[-1] = tuple(l[-1])
        l.append([])
    l[-1].append(i)
print(l[1:])

    Output:

    [(('item', '10 Hz'), ('value', 10), ('align', 'left'), ('hidden', 1)), (('item', '20 Hz'), ('value', 20), ('align', 'right')), (('item', '50 Hz'), ('value', 50)), [('item', '100 Hz'), ('value', 100), ('textColor', 16711680)]]

    The only disadvantage of this method is that you need to remove the first element of the output list of tuples, so it may doesn't work in certain situations.