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Roadmap page has numbered-only list when should be a mix of numbered and unnumbered #60913

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rffontenelle opened this issue Feb 11, 2025 · 1 comment
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@rffontenelle
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about / roadmap page in the website shows a numbered list of 17 items and this doesn't seem to be the expected result by looking at the code:

1. Label indexing must never involve looking in an axis twice for the same label(s).
This implies that any validation step must either:
* limit validation to general features (e.g. dtype/structure of the key/index), or
* reuse the result for the actual indexing.
2. Indexers must never rely on an explicit call to other indexers.
For instance, it is OK to have some internal method of `.loc` call some
internal method of `__getitem__` (or of their common base class),
but never in the code flow of `.loc` should `the_obj[something]` appear.
3. Execution of positional indexing must never involve labels (as currently, sadly, happens).
That is, the code flow of a getter call (or a setter call in which the right hand side is non-indexed)
to `.iloc` should never involve the axes of the object in any way.
4. Indexing must never involve accessing/modifying values (i.e., act on `._data` or `.values`) more than once.
The following steps must hence be clearly decoupled:
* find positions we need to access/modify on each axis
* (if we are accessing) derive the type of object we need to return (dimensionality)
* actually access/modify the values
* (if we are accessing) construct the return object
5. As a corollary to the decoupling between 4.i and 4.iii, any code which deals on how data is stored
(including any combination of handling multiple dtypes, and sparse storage, categoricals, third-party types)
must be independent from code that deals with identifying affected rows/columns,
and take place only once step 4.i is completed.
* In particular, such code should most probably not live in `pandas/core/indexing.py`
* ... and must not depend in any way on the type(s) of axes (e.g. no `MultiIndex` special cases)
6. As a corollary to point 1.i, `Index` (sub)classes must provide separate methods for any desired validity check of label(s) which does not involve actual lookup,
on the one side, and for any required conversion/adaptation/lookup of label(s), on the other.
7. Use of trial and error should be limited, and anyway restricted to catch only exceptions
which are actually expected (typically `KeyError`).
* In particular, code should never (intentionally) raise new exceptions in the `except` portion of a `try... exception`

@michellesweering
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