next round of updates (small text updates, add capitalized String alias)

Author: jorisvandenbossche

web/pandas/pdeps/0014-string-dtype.md

@@ -12,7 +12,7 @@ This PDEP proposes to introduce a dedicated string dtype that will be used by
 default in pandas 3.0:
 
 * In pandas 3.0, enable a "string" dtype by default, using PyArrow if available
-  or otherwise the numpy object-dtype alternative.
+  or otherwise a string dtype using numpy object-dtype under the hood as fallback.
 * The default string dtype will use missing value semantics (using NaN) consistent
   with the other default data types.
 
@@ -69,11 +69,11 @@ data type in pandas that is not backed by Python objects.
 After acceptance of PDEP-10, two aspects of the proposal have been under
 reconsideration:
 
-- Based on user feedback (mostly around installation complexity and size), it
-  has been considered to relax the new `pyarrow` requirement to not be a _hard_
-  runtime dependency. In addition, NumPy 2.0 could in the future potentially
-  reduce the need to make PyArrow a required dependency specifically for a
-  dedicated pandas string dtype.
+- Based on feedback from users and maintainers from other packages (mostly
+  around installation complexity and size), it has been considered to relax the
+  new `pyarrow` requirement to not be a _hard_ runtime dependency. In addition,
+  NumPy 2.0 could in the future potentially reduce the need to make PyArrow a
+  required dependency specifically for a dedicated pandas string dtype.
 - PDEP-10 did not consider the usage of the experimental `pd.NA` as a
   consequence of adopting one of the existing implementations of the
   `StringDtype`.
@@ -250,22 +250,24 @@ in flux (eventually making pyarrow a required dependency? adopting `pd.NA` as
 the default missing value sentinel? using the new NumPy 2.0 capabilities?
 overhauling all our dtypes to use a logical data type system?), introducing a
 default string dtype could also be delayed until there is more clarity in those
-other discussions.
+other discussions. Specifically, it would avoid temporarily switching to use
+`NaN` for the string dtype, while in a future version we might switch back
+to `pd.NA` by default.
 
 However:
 
 1. Delaying has a cost: it further postpones introducing a dedicated string
    dtype that has massive benefits for users, both in usability as (for the
-   significant part of the user base that has PyArrow installed) in performance.
+   part of the user base that has PyArrow installed) in performance.
 2. In case pandas eventually transitions to use `pd.NA` as the default missing value
    sentinel,  a migration path for _all_ pandas data types will be needed, and thus
    the challenges around this will not be unique to the string dtype and
    therefore not a reason to delay this.
 
 Making this change now for 3.0 will benefit the majority of users, while coming
 at a cost for a part of the users who already started using the `"string"` or
-`pd.StringDtype()` dtype (they will have to update their code to continue to the
-variant using `pd.NA`, see the "Backward compatibility" section below).
+`pd.StringDtype()` dtype (they will have to update their code to continue to use
+the variant using `pd.NA`, see the "Backward compatibility" section below).
 
 ### Why not use the existing StringDtype with `pd.NA`?
 
@@ -311,9 +313,14 @@ To allow testing code in advance, the
 `pd.options.future.infer_string = True` option is available for users.
 
 Otherwise, the actual string-specific functionality (such as the `.str` accessor
-methods) should generally all keep working as is. By preserving the current
-missing value semantics, this proposal is also backwards compatible on this
-aspect.
+methods) should generally all keep working as is.
+
+By preserving the current missing value semantics, this proposal is also mostly
+backwards compatible on this aspect. When storing strings in object dtype, pandas
+however did allow using `None` as the missing value indicator as well (and in
+certain cases such as the `shift` method, pandas even introduced this itself).
+For all the cases where currently `None` was used as the missing value sentinel,
+this will change to use `NaN` consistently.
 
 ### For existing users of `StringDtype`
 
@@ -359,17 +366,18 @@ options:
 - If the user specifically wants the variant of the string dtype that uses
   `pd.NA` (and returns nullable numeric/boolean dtypes in operations), they will
   have to update their dtype specification from `"string"` / `pd.StringDtype()`
-  to `pd.StringDtype(na_value=pd.NA)` to suppress the warning and further keep
-  their code running as is.
+  to `"String"` / `pd.StringDtype(na_value=pd.NA)` to suppress the warning and
+  further keep their code running as is.
+
+A `"String"` alias (capitalized) would be added to make it easier for users to
+continue using the variant using `pd.NA`, and such capitalized string alias is
+consistent with other nullable dtypes (`"float64`" vs `"Float64"`).
 
 ## Timeline
 
 The future PyArrow-backed string dtype was already made available behind a feature
 flag in pandas 2.1 (enabled by `pd.options.future.infer_string = True`).
 
-Some small enhancements or fixes might still be needed and can continue to be
-backported to pandas 2.2.x.
-
 The variant using numpy object-dtype can also be backported to the 2.2.x branch
 to allow easier testing. It is proposed to release this as 2.3.0 (created from
 the 2.2.x branch, given that the main branch already includes many other changes