When and why should I use a namedtuple instead of a dictionary?

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What are “named tuples” in Python?

What is the situation where a namedtuple should be used?

When I looked into it, it looked like a way to make tuples more like dictionaries. How do they compare to dictionaries?

Can only the same hashable types for dictionaries be used for namedtuples?

Take a look at this question - http://stackoverflow.com/questions/2970608/what-are-named-tuples-in-python — ronakg, Mar 26 '12 at 12:45
This is not a duplicate of [the question mentioned above](https://stackoverflow.com/questions/2970608/what-are-named-tuples-in-python). The two are complementary. — djvg, Feb 07 '18 at 13:52
^-- agreed: [2970608](http://stackoverflow.com/questions/2970608/what-are-named-tuples-in-python) has named tuple FAQs and this one asks for comparison to dict. — Tom Hundt, Apr 04 '18 at 16:39

score 260 · Accepted Answer · answered Mar 26 '12 at 12:49

260

In dicts, only the keys have to be hashable, not the values. namedtuples don't have keys, so hashability isn't an issue.

However, they have a more stringent restriction -- their key-equivalents, "field names", have to be strings.

Basically, if you were going to create a bunch of instances of a class like:

class Container:
    def __init__(self, name, date, foo, bar):
        self.name = name
        self.date = date
        self.foo = foo
        self.bar = bar

mycontainer = Container(name, date, foo, bar)

and not change the attributes after you set them in __init__, you could instead use

Container = namedtuple('Container', ['name', 'date', 'foo', 'bar'])

mycontainer = Container(name, date, foo, bar)

as a replacement.

Of course, you could create a bunch of dicts where you used the same keys in each one, but assuming you will have only valid Python identifiers as keys and don't need mutability,

mynamedtuple.fieldname

is prettier than

mydict['fieldname']

and

mynamedtuple = MyNamedTuple(firstvalue, secondvalue)

is prettier than

mydict = {'fieldname': firstvalue, 'secondfield': secondvalue}

Finally, namedtuples are ordered, unlike regular dicts, so you get the items in the order you defined the fields, unlike a dict.

answered Mar 26 '12 at 12:49

agf

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Also, quoting Raymondh: "Instances of named tuples use no more space than regular tuples. The field name properties are stored in the namedtuple class." https://twitter.com/raymondh/status/524660721968107521 – Moberg Oct 31 '14 at 07:48
6

One more thing to note is that the named tuple can also be initialized as `mynamedtuple = MyNamedTuple(fieldname=firstvalue, secondfield=secondvalue)` – Bharat Khatri Feb 10 '18 at 09:55
2

You can make the instantiatiation even prettier/simpler with `Container = namedtuple('Container', 'name date foo bar')` – stackPusher Mar 15 '18 at 15:49
1

If you need more flexibility, [attrs](http://www.attrs.org/en/stable/why.html#namedtuples) is an interesting alternative to namedtuple. – Christian Long Aug 14 '18 at 15:11
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If you're using Python 3.7 or CPython 3.6 `dicts` are [insertion ordered](https://stackoverflow.com/questions/39980323/are-dictionaries-ordered-in-python-3-6). – Boris Verkhovskiy Jan 27 '19 at 21:18
1

@Boris Good info, but still different from field definition ordering and in many situations just as unknown as random ordering. – agf Jan 28 '19 at 11:18

score 46 · Answer 2 · answered Mar 26 '12 at 12:47

46

Tuples are immutable, whether named or not. namedtuple only makes the access more convenient, by using names instead of indices. You can only use valid identifiers for namedtuple, it doesn't perform any hashing — it generates a new type instead.

answered Mar 26 '12 at 12:47

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When and why should I use a namedtuple instead of a dictionary?

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