Printing list items by group in python

I’m still new to Python. I have similar list to the below list:

items = [[4, 'A'], [4, 'B'], [5, 'C'], [5, 'D'], [5, 'E'], [6, 'F'], [6, 'G']]

I’m trying to print it by grouping the first item together and get something like this:

4 : ['A', 'B']
5 : ['C', 'D', 'E']
6 : ['F', 'G']

How do I do this?

Answer

You can use itertools.groupby and operator.itemgetter:

>>> from itertools import groupby
>>> from operator import itemgetter
>>> list_ = [[4, 'A'], [4, 'B'], [5, 'C'], [5, 'D'], [5, 'E'], [6, 'F'], [6, 'G']]
>>> print(*(f'{k}: {sum(list(g), [])}' 
            for k, g in groupby(list_, key=lambda x: list.pop(x, 0))), 
           sep='n')
4: ['A', 'B']
5: ['C', 'D', 'E']
6: ['F', 'G']

If you want to do this without importing anything:

>>> list_ = [[4, 'A'], [4, 'B'], [5, 'C'], [5, 'D'], [5, 'E'], [6, 'F'], [6, 'G']]

>>> table = {}

>>> for key, value in list_:
        table.setdefault(key, []).append(value)
    

>>> table
{4: ['A', 'B'], 5: ['C', 'D', 'E'], 6: ['F', 'G']}

>>> for key, group in table.items():
        print(f'{key}: {group}')
    
4: ['A', 'B']
5: ['C', 'D', 'E']
6: ['F', 'G']