python: approaches to sort a list of dictionaries

sort-list-of-dictionaries.py

#!/usr/bin/python

from __future__ import print_function

# from https://wiki.python.org/moin/SortingListsOfDictionaries
def multikeysort(items, columns):
    from operator import itemgetter
    comparers = [ ((itemgetter(col[1:].strip()), -1) if col.startswith('-') else (itemgetter(col.strip()), 1)) for col in columns]
    def comparer(left, right):
        for fn, mult in comparers:
            result = cmp(fn(left), fn(right))
            if result:
                return mult * result
        else:
            return 0
    return sorted(items, cmp=comparer)


if __name__ == "__main__":
    a = {"key1": 5 , "key2": 8, "key3": 2}
    b = {"key1": 7 , "key2": 4, "key3": 9}
    c = {"key1": 6 , "key2": 1, "key3": 1}
    masterList = [a, b, c]

    sortedList = multikeysort(masterList, ['key1', 'key2', 'key3'])

    keys = ('key1', 'key2', 'key3')

    print("Original unsorted list:")
    for i in masterList:
        row = [ str(i[k]) for k in keys ]
        print( "\t", "\t".join(row) )

    print("Sorted list:")
    for i in sortedList:
        row = [ str(i[k]) for k in keys ]
        print( "\t", "\t".join(row) )

    # Another alternative approach (1)
    # # Sort by multiple keys - case sensitive
    # from operator import itemgetter
    # mylist = sorted(mylist, key=itemgetter('name', 'age'))

    # # Sort by multiple keys - case insensitive
    # mylist = sorted(mylist, key=lambda k: (k['name'].lower(), k['age']))

    # Another alternative approach (2)
    # Schwartzian Transform in python
    # sort_on = "key2"
    # decorated = [(dict_[sort_on], dict_) for dict_ in undecorated]
    # decorated.sort()
    # result = [dict_ for (key, dict_) in decorated]