It seems to me that NamedTuple
and TypedDict
are fairly similar and the Python developers themselves recognized that.
Concerning the PEP, I would rather add a common section about NamedTuple and TypedDict, they are quite similar and the latter already behaves structurally. What do you think? source
But then Guido seems not so sure about that.
I'm not so sure that NamedTuple and TypedDict are really all that similar (except they are both attempts to handle outdated patterns in a statically-typed world).
source
So, this is my lazy attempt to get someone else come up with a crisp comparison where the official documentation seems lacking.
TypedDict was introduced in Python 3.8 to provide type Hints for Dictionaries with a Fixed Set of Keys. The TypedDict allows us to describe a structured dictionary/map with an expected set of named string keys mapped to values of particular expected types, which Python type-checkers like mypy can further use.
Python namedtuple is an immutable container type, whose values can be accessed with indexes and named attributes. It has functionality like tuples with additional features. A named tuple is created with the collections. namedtuple factory function.
Named Tuple Python's tuple is a simple data structure for grouping objects with different types. Its defining feature is being immutable.
Python and its community are wrestling with the "struct" problem: how to best group related values into composite data objects that allow logical/easy accessing of components (typically by name). There are many competing approaches:
collections.namedtuple
instancestuple
and list
with implied meanings for each position/slot (archaic but extremely common)So much for "There should be one—and preferably only one—obvious way to do it."
Both the typing
library and Mypy, like the Python community at large, are simultaneously struggling with how to more effectively define types/schema, including for composite objects. The discussion you linked to is part of that wrestling and trying to find a way forward.
NamedTuple
is a typing superclass for structured objects resulting from the collections.namedtuple
factory; TypedDict
a Mypy attempt to define the keys and corresponding types of values that occur when using fixed-schema dictionaries. They are similar if you're just thinking about "I have a fixed set of keys that should map to a fixed set of typed values." But the resulting implementations and constraints are very different. Are a bag and a box similar? Maybe. Maybe not. Depends on your perspective and how you want to use them. Pour wine and let the discussion begin!
NamedTuple
, by the way, is now a formal part of Python.
from typing import NamedTuple class Employee(NamedTuple): name: str id: int
TypedDict
started life as an experimental Mypy feature to wrangle typing onto the heterogeneous, structure-oriented use of dictionaries. As of Python 3.8, however, it was adopted into the standard library.
try: from typing import TypedDict # >=3.8 except ImportError: from mypy_extensions import TypedDict # <=3.7 Movie = TypedDict('Movie', {'name': str, 'year': int})
A class-based type constructor is also available:
class Movie(TypedDict): name: str year: int
Despite their differences, both NamedTuple
and TypedDict
lock down the specific keys to be used, and the types of values corresponding to each key. Therefore they are aiming at basically the same goal: Being useful typing mechanisms for composite/struct types.
Python's standard typing.Dict
focuses on much more homogenous, parallel mappings, defining key/value types, not keys per se. Therefore it is not very useful in defining composite objects that happen to be stored in dictionaries.
ConnectionOptions = Dict[str, str]
There are a couple of minor differences. Note that those containers haven't been there forever:
I would go for NamedTuple
if possible and if I want the values to be frozen. Otherwise I would use a dataclass.
from dataclasses import dataclass from typing import NamedTuple, TypedDict from enum import Enum class Gender(Enum): MALE = "male" FEMALE = "female" ## Class definition: Almost the same @dataclass class UserDataC: name: str gender: Gender class UserTuple(NamedTuple): name: str gender: Gender class UserNDict(TypedDict): name: str gender: Gender ## Object Creation: Looks the same anna_datac = UserDataC(name="Anna", gender=Gender.FEMALE) anna_tuple = UserTuple(name="Anna", gender=Gender.FEMALE) anna_ndict = UserNDict(name="Anna", gender=Gender.FEMALE) ## Mutable values vs frozen values anna_datac.gender = Gender.MALE # anna_tuple.gender = Gender.MALE # AttributeError: can't set attribute anna_ndict["gender"] = Gender.MALE # AttributeError: 'dict' object has no attribute 'gender' # anna_ndict.gender = Gender.MALE ## New attribute # Note that you can add new attributes like this. # Python will not complain. But mypy will. anna_datac.password = "secret" # Dataclasses are extensible # anna_tuple.password = "secret" # AttributeError - named tuples not # anna_ndict.password = "secret" # AttributeError - TypedDict not anna_ndict["password"] = "secret" ## isinstance assert isinstance(anna_tuple, tuple) assert isinstance(anna_ndict, dict)
I think it's more intuitive to write and read. Plus you give mypy more possibilities to check:
class UserTuple(NamedTuple): name: str gender: Gender # vs UserTuple = namedtuple("UserTuple", ["name", "gender"])
If I don't need things to be mutable, I like if they are not. This way I prevent unexpected side effects
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With