Improved performance and arguably simpler code for dictionaries by changing the keys layout
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- Dominant language
- Python
- Stars
- 77.2k
- Forks
- 35.9k
- PR merge metrics
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Description
Current layout
Currently the _dictkeysobject struct is laid out like this:
ptr ----> +--------------+
| header |
+--------------+
| indices |
+--------------+
| keys |
+--------------+
which requires some relatively expensive calculation to find the start of the keys, as the indices are not only variable in number, but variable in size also.
Proposed layout
If instead it is laid out as follows:
+--------------+
| indices |
ptr ----> +--------------+
| header |
+--------------+
| keys |
+--------------+
and the indices laid from highest to lowest with 0 just before ptr, finding the start of the keys is as simple as ptr->keys . Accessing an index is no slower, and the code barely any more complex.
Linked PRs
- gh-145097
- gh-150640
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Review the proposed _dictkeysobject layout and the linked PRs gh-145097 and gh-150640 first, since the work has moved there. Compare the current and proposed index, header, and keys arrangement; completion would require the implementation and its performance or correctness validation to support the new layout.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- backend
- Issue type
- Refactor
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100