+1 to the idea in principle. It can easily be implemented in a dynamic type checker (my area of interest). Some thought will need to be put into how subclassing should work (similar to the current "total" inheritance situation).  Paul P.S. I was tempted to suggest some kind of wildcard key or key pattern matching, but I think that deviates from the relatively simple solution you're suggesting. On Wed, 2021-04-07 at 15:09 +0800, NGC4039 wrote:

For a third-party type checker, only the type of the value corresponding to the defined key needs to be checked, and the value type of the undefined key only needs to be deduced to non-existent (just like https://www.python.org/dev/peps/pep-0655/) or Any type.

------------------ 原始邮件 ------------------ 发件人: "Paul Bryan" <pbryan@anode.ca>; 发送时间: 2021年4月7日(星期三) 下午3:03 收件人: "typing-sig"<typing-sig@python.org>;

主题: [Typing-sig] Re: 回复：[Typing-sig] Re: More forgiving TypedDict?

Sorry, I didn't read the second part of your answer (constraining types for certain keys) before I replied.

Q3. Are you expecting that a static type checker will constrain such types?

Paul

On Tue, 2021-04-06 at 23:59 -0700, Paul Bryan wrote:

...

Ah, non-str values in WSGI environ. Thanks. So, rephrasing my second question:

Q2: Since environ keys must be str, and as you don't want to validate the keys, what is the value of using TypedDict[...] over, say, dict[str, Any]?

Paul

On Wed, 2021-04-07 at 14:49 +0800, NGC4039 wrote:

...

I think the value type of the undefined key should be Any.

The significance of the TypedDict that allows undefined keys is that we can constrain the types of some keys and values.

------------------ 原始邮件 ------------------ 发件人: "Paul Bryan" <pbryan@anode.ca>; 发送时间: 2021年4月7日(星期三) 下午2:42 收件人: "NGC4039"<me@abersheeran.com>;"typing-sig"<typing- sig@python.org>;

主题: [Typing-sig] Re: More forgiving TypedDict?

As you point out, TypedDict was proposed to explicitly reject an invalid key.

Q1: In your view, would allowing undefined keys simply allow any undefined key to be considered valid, regardless of value?

Q2: Since environ keys and values must be str, and as you don't want to validate the keys, what is the value of using TypedDict[...] over, say, dict[str, str]?

Paul

On Wed, 2021-04-07 at 14:00 +0800, Aber wrote: Hey, everyone.

When writing a more static WSGI definition based on PEP3333, I discovered such a problem. TypedDict cannot describe the HTTP_* keys in the WSGI specification. I know that one of the original intentions of TypedDict is to prevent typing the wrong keys. But can we add an option (for example: allow_undefined=True) to allow this actual problem?

Now the definition I wrote is here https://gist.github.com/abersheeran/f3723029387fe7f6584c6b157b90a 50a In order to allow undefined key values to be used, such as `HTTP_HOST`, perhaps it can be used like the following (there is currently no specification, this is just the solution I envisioned).

```python class Environ(CGIRequiredDefined, CGIOptionalDefined, WSGIDefined, allow_undefined=True):     """     WSGI Environ     """ ```

Or is there a solution that I don’t know?

--- Aber

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