Operator.itemgetter

New In Python 2.4

Changed In Python 2.5: Added support for multiple item extraction.

Operator.itemgetter

operator.itemgetter(item)

operator.itemgetter(*items)

Return a callable object that fetches item from its operand using the operand’s __getitem__() method. If multiple items are specified, returns a tuple of lookup values. For example:

After f = itemgetter(2), the call f(r) returns r[2].
After g = itemgetter(2, 5, 3), the call g(r) returns (r[2], r[5], r[3]).

Equivalent to:

def itemgetter(*items):
    if len(items) == 1:
        item = items[0]
        def g(obj):
            return obj[item]
    else:
        def g(obj):
            return tuple(obj[item] for item in items)
    return g

The items can be any type accepted by the operand’s __getitem__() method. Dictionaries accept any hashable value. Lists, tuples, and strings accept an index or a slice:

>>> itemgetter(1)('ABCDEFG')
'B'
>>> itemgetter(1,3,5)('ABCDEFG')
('B', 'D', 'F')
>>> itemgetter(slice(2,None))('ABCDEFG')
'CDEFG'

Sorted

In [19]: a = {'Huang': ['Kimi', 1988], 'Li': ['Robbin', 1968]}

In [20]: # Order By Year

In [21]: import operator

In [22]: sorted(a.iteritems(), key=lambda(k, v): operator.itemgetter(1)(v))
Out[22]: [('Li', ['Robbin', 1968]), ('Huang', ['Kimi', 1988])]

In [23]: # Order By (Name, Year)

In [24]: sorted(a.iteritems(), key=lambda(k, v): operator.itemgetter(0, 1)(v))
Out[24]: [('Huang', ['Kimi', 1988]), ('Li', ['Robbin', 1968])]

Multi Sort

Python has a stable sort. So it's safe to sort one by one.

In [33]: list1 = sorted(a.iteritems(), key=lambda(k, v): operator.itemgetter(0)(v))

In [34]: list1 = sorted(list1, key=lambda(k, v): operator.itemgetter(1)(v))

References

[1] Docs@Python, 9.9. operator — Standard operators as functions

[2] half full@StackOverflow, Sorting a Python list by two criteria

Operator.itemgetter

Operator.itemgetter