fix(shared/functions): fix slice_dictionary implementation

[Liam-DeVoe]

Issue number: #7252

The implementation of slice_dictionary has a bug: it will keep repeating the first chunk, because the stop index chunk_size is not incremented as it iterates.

import itertools

def slice_dictionary(data: dict, chunk_size: int):
    for _ in range(0, len(data), chunk_size):
        yield {dict_key: data[dict_key] for dict_key in itertools.islice(data, chunk_size)}

data = {"k0": 0, "k1": 1, "k2": 2}
# actual   [{'k0': 0, 'k1': 1}, {'k0': 0, 'k1': 1}]
# expected [{'k0': 0, 'k1': 1}, {'k2': 2}]
print(list(slice_dictionary(data, 2)))

fwiw: I found this bug during a research project I'm working on which uses LLMs to write property-based tests in Hypothesis. A property which found this bug was proposed and written "autonomously" by the agent. I wrote this PR myself and take full responsibility for it.

---

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[boring-cyborg]

Thanks a lot for your first contribution! Please check out our contributing guidelines and don't hesitate to ask whatever you need.
In the meantime, check out the #python channel on our Powertools for AWS Lambda Discord: Invite link

[anafalcao]

Hey @tybug ! Thank you so much for opening this PR, we’ll review it and get back to you.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.35%. Comparing base (3aada65) to head (ca8c2b7).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #7246   +/-   ##
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  Coverage    96.35%   96.35%           
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  Files          275      275           
  Lines        12980    12980           
  Branches       965      965           
========================================
  Hits         12507    12507           
  Misses         366      366           
  Partials       107      107           

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[leandrodamascena]

fwiw: I found this bug during a research project I'm working on which uses LLMs to write property-based tests in Hypothesis. A property which found this bug was proposed and written "autonomously" by the agent. I wrote this PR myself and take full responsibility for it.

(By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.)

Hey @tybug this code looks good to me. But I'm curious about the hypothesis you created. I have plans to introduce hypothesis framework in this project to exactly cover cases like this. Do you have a minimal repository where I can those tests?

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[leandrodamascena]

Thanks a lot for working on this @Liam-DeVoe! APPROVED

[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!

[Liam-DeVoe]

I have plans to introduce hypothesis framework in this project to exactly cover cases like this. Do you have a minimal repository where I can those tests?

As a Hypothesis maintainer, that makes me very happy to hear :)

Here's the full bug report written autonomously by the agent, which has the property-based test it wrote inside it:
bug_report_slice_dictionary_2025-08-18_23-20_k8f3.md.

This test is...fine, but it's not particularly idiomatic. The way I might write it instead is:

from hypothesis import given, strategies as st
from aws_lambda_powertools.shared.functions import slice_dictionary

@given(
    st.dictionaries(st.text(), st.integers()),
    st.integers(min_value=1)
)
def test(data, chunk_size):
    if not data:
        chunks = list(slice_dictionary(data, chunk_size))
        assert chunks == []
        return

    chunks = list(slice_dictionary(data, chunk_size))

    reconstructed = {}
    for chunk in chunks:
        reconstructed.update(chunk)

    assert reconstructed == data

and possibly the empty-list case could be removed/folded into the standard property as well (I would have to think about it a bit more).