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?
- 2Take a look at this question - stackoverflow.com/questions/2970608/…ronakg– ronakg2012-03-26 12:45:41 +00:00Commented Mar 26, 2012 at 12:45
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2 Answers
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.
7 Comments
Moberg
Also, quoting Raymondh: "Instances of named tuples use no more space than regular tuples. The field name properties are stored in the namedtuple class." twitter.com/raymondh/status/524660721968107521
Bharat Khatri
One more thing to note is that the named tuple can also be initialized as
mynamedtuple = MyNamedTuple(fieldname=firstvalue, secondfield=secondvalue)
stackPusher
You can make the instantiatiation even prettier/simpler with
Container = namedtuple('Container', 'name date foo bar')
Christian Long
If you need more flexibility, attrs is an interesting alternative to namedtuple.
If you're using Python 3.7 or CPython 3.6
dicts are insertion ordered. |
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.
