# PEP 728: TypedDict with Typed Extra Items

**URL:** <https://discuss.python.org/t/pep-728-typeddict-with-typed-extra-items/45443>\
**Category:** PEPs\
**Tags:** typing\
**Created:** [February 9, 2024, 5:20am UTC](https://discuss.python.org/t/pep-728-typeddict-with-typed-extra-items/45443 "2024-02-09T05:20:20Z")\
**Posts on this page:** 1\
**Showing post:** 24

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**Author:** ![erictraut](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/erictraut/32/15190_2.png) [@erictraut](https://discuss.python.org/u/erictraut)\
**Post date:** [February 9, 2024, 8:53pm UTC](https://discuss.python.org/t/pep-728-typeddict-with-typed-extra-items/45443/24 "2024-02-09T20:53:52Z")

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Here are a couple of additional ideas to throw into the mix.

* * *

The first idea involves the use of a method declaration within a TypedDict.

Currently, TypedDict definitions don’t allow any method declarations. We could specify that a ` __closed__ ` method can be declared that returns the type of the allowed ‘extra’ attributes.

```python
class Point(TypedDict):
    x: float
    y: float
    def __closed__ (self) -> Never: ...

```

This idea has the benefit of not affecting backward compatibility.

The downsides are that it’s probably not what most Python developers would expect. It’s also not clear how this would work with the functional form of `TypedDict`.

* * *

The second idea involves the use of a new parameter to the `TypedDict` constructor named `closed`. If set to `True`, the `TypedDict` would be considered “closed” in that type checkers should assume that no additional items are allowed. If a user wants to allow additional items of a specific type, they would additionally include an ` __extra__ : <type>` attribute declaration. If no ` __extra__ ` is present but `closed` is set to `True`, it acts as though an implicit ` __extra__ : Never` is present.

```python
class Point1(TypedDict, closed=True):
    x: float
    y: float

class Point2(TypedDict, closed=True):
    x: float
    y: float
    __extra__ : int

```

I think this construct feels pretty natural — especially in the common case where the user simply wants to specify that no other items can be present. It also preserves backward compatibility and works with the functional form. It could also be made to work with a potential future inlined version (by special-casing ` __extra__ ` in the inlined version).

In the (extremely unlikely) event that you want to create a closed TypedDict with a key named ` __extra__ `, you could do so through inheritance.

```python
# Create a non-closed TypedDict that includes ` __extra__ ` item
class TDWithExtra(TypedDict):
    x: float
    y: float
    __extra__ : float

# Create a closed version of the above
class ClosedTDWithExtra1(TDWithExtra, closed=True):
    ...

# Or a closed version with extra items
class ClosedTDWithExtra2(TDWithExtra, closed=True):
    __extra__ : int

```

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_[View the full topic](https://discuss.python.org/t/pep-728-typeddict-with-typed-extra-items/45443)._