DEP: records: Deprecate treating shape=0 as shape=None

`shape=n` is a shorthand for `shape=(n,)` except in the case when `n==0`, when it is a shorthand for `shape=None`.

This special case is dangerous, as it makes `fromrecords(..., shape=len(a))` behave surprisingly when a is an empty sequence.

Users impacted by this warning either:
* Have a bug in their code, and will need to either:
  - wait for the deprecation to expire
  - change their code to use `(len(a),)` instead of `len(a)`
* Are using the non-preferred spellling, and will need to replace a literal `0` or `False` with `None`

1 files changed, 11 insertions, 0 deletions

diff --git a/doc/release/upcoming_changes/15217.deprecation.rst b/doc/release/upcoming_changes/15217.deprecation.rst
new file mode 100644
index 000000000..e9dd0995d
--- /dev/null
+++ b/doc/release/upcoming_changes/15217.deprecation.rst
@@ -0,0 +1,11 @@
+Passing ``shape=0`` to factory functions in ``numpy.rec`` is deprecated
+-----------------------------------------------------------------------
+
+``0`` is treated as a special case by these functions, which aliases to
+``None``. In future, ``0`` will not be a special case, and will be treated
+as an array length like any other integer is. The affected functions are:
+
+* `numpy.core.records.fromarrays`
+* `numpy.core.records.fromrecords`
+* `numpy.core.records.fromstring`
+* `numpy.core.records.fromfile`