Question

The standard library namedtuple class looks to me like a way to make tuples more like dictionaries. How do namedtuples compare to dicts? When should we use them? Do they work with non-hashable types?

Answer 1

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.