hash map

[isidroas]

• Mutable _Item
• document falsy item
• resize_down: expected test result
• resize_down: actual result

Please refer to the commit messages for a detailed breakdown of the changes.

Feedback from the original author, @Cjkjvfnby, would be greatly appreciated!

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".

[Cjkjvfnby]

Thank you for improving it.

Changes look good, I left some cosmetic comments.

As for making _Item mutable, Immutability gives extra protection in exchange for performance. In this abstract case, I don't have any strong preference, both versions are fine.

[Cjkjvfnby]

Can we go with size 4? In that case, we could avoid the loop.

[isidroas]

Something like this?

# Test resize down when sparse
## Setup: resize up
>>> hm = HashMap(4, capacity_factor=0.75)
>>> len(hm._buckets)
4
>>> hm[0] = 0
>>> hm[1] = 1
>>> hm[2] = 2
>>> len(hm._buckets)
4
>>> hm[3] = 3
>>> len(hm._buckets)
8

## Resize down
>>> del hm[3]
>>> len(hm._buckets)
8
>>> del hm[2]
>>> len(hm._buckets)
4

I've checked that it passes, but I don't know which one I prefer

[Cjkjvfnby]

I'd prefer to keep tests as linear as possible.

[Cjkjvfnby]

Let's wait for the 3d opinion.

[isidroas]

Thank you for improving it.

Changes look good, I left some cosmetic comments.

Thank you for the revision!

As for making _Item mutable, Immutability gives extra protection in exchange for performance. In this abstract case, I don't have any strong preference, both versions are fine.

I understand that the immutable version is faster. That said, performance will be limited in Python either way

[Cjkjvfnby]

Changes look good. I'll not be active for the next 2 weeks, please don't wait for me.