fix: remove python-dateutil runtime dependency

[marandaneto]

💡 Motivation and Context

Fixes #109.

python-dateutil was a runtime dependency of the SDK, and older supported dependency resolutions can emit Python 3.12+ deprecation warnings on import. The SDK only used a small subset of dateutil behavior, so this removes it from runtime dependencies while keeping compatibility covered in tests.

💚 How did you test it?

• uv run ruff check posthog sdk_compliance_adapter
• uv run pytest -q
• uv run mypy --no-site-packages --config-file mypy.ini . | uv run mypy-baseline filter
• uv run python -W error::DeprecationWarning -c 'import posthog'

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file
• Added the release label to the PR

[greptile-apps]

Prompt To Fix All With AI

This is a comment left during a code review.
Path: posthog/feature_flags.py
Line: 777-787

Comment:
**`fromisoformat` rejects space-separated timezone offsets on Python 3.10**

`datetime.fromisoformat` on Python 3.10 does not accept a space between the time and the UTC-offset (e.g. `"2022-04-05 12:34:12 +01:00"`), raising a `ValueError`. Python 3.11 expanded `fromisoformat` to accept most ISO 8601 forms, but since `requires-python = ">=3.10"`, any property value string in that format will fail on 3.10 where `dateutil.parser.parse` previously succeeded. The test `test_parse_datetime_matches_dateutil_for_supported_formats` itself includes this exact case, so it will only pass on 3.11+. A simple normalisation before calling `fromisoformat` would cover it:

```python
def parse_datetime(value: str) -> datetime.datetime:
    text = value.strip()
    if text.endswith("Z"):
        text = text[:-1] + "+00:00"
    elif text.upper().endswith(" UTC"):
        text = text[:-4] + "+00:00"
    elif re.fullmatch(r"\d{4}", text):
        now = datetime.datetime.now()
        return datetime.datetime(int(text), now.month, now.day)
    # Normalise "... +HH:MM" (space before offset) accepted by dateutil but not
    # by fromisoformat on Python < 3.11.
    text = re.sub(r" ([+-]\d{2}:\d{2})$", r"\1", text)
    return datetime.datetime.fromisoformat(text)
```

How can I resolve this? If you propose a fix, please make it concise.

---

This is a comment left during a code review.
Path: posthog/test/test_feature_flags.py
Line: 4582-4589

Comment:
**Prefer parameterised test**

Per the project's simplicity rules, parameterised tests are preferred. The loop over a tuple of strings is equivalent to a parameterised test but hides failures behind a single test name and stops on the first failure, making it harder to diagnose which format broke.

```python
@parameterized.expand([
    ("iso_date", "2022-05-01"),
    ("iso_datetime_Z", "2022-04-05T12:34:12Z"),
    ("iso_datetime_utc", "2022-04-05 12:34:12 UTC"),
    ("iso_datetime_offset", "2022-04-05 12:34:12 +01:00"),
])
def test_parse_datetime_matches_dateutil_for_supported_formats(self, _name, value):
    assert parse_datetime(value) == parser.parse(value)
```

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "fix: remove python-dateutil runtime depe..." | Re-trigger Greptile}

[github-actions]

posthog-python Compliance Report

Date: 2026-04-28 14:46:23 UTC
Duration: 159947ms

✅ All Tests Passed!

30/30 tests passed

---

Capture Tests

✅ 29/29 tests passed

View Details

Test	Status	Duration
Format Validation.Event Has Required Fields	✅	515ms
Format Validation.Event Has Uuid	✅	1505ms
Format Validation.Event Has Lib Properties	✅	1505ms
Format Validation.Distinct Id Is String	✅	1505ms
Format Validation.Token Is Present	✅	1505ms
Format Validation.Custom Properties Preserved	✅	1505ms
Format Validation.Event Has Timestamp	✅	1505ms
Retry Behavior.Retries On 503	✅	9511ms
Retry Behavior.Does Not Retry On 400	✅	3508ms
Retry Behavior.Does Not Retry On 401	✅	3506ms
Retry Behavior.Respects Retry After Header	✅	9512ms
Retry Behavior.Implements Backoff	✅	23520ms
Retry Behavior.Retries On 500	✅	7506ms
Retry Behavior.Retries On 502	✅	7509ms
Retry Behavior.Retries On 504	✅	7505ms
Retry Behavior.Max Retries Respected	✅	23529ms
Deduplication.Generates Unique Uuids	✅	1494ms
Deduplication.Preserves Uuid On Retry	✅	7513ms
Deduplication.Preserves Uuid And Timestamp On Retry	✅	14517ms
Deduplication.Preserves Uuid And Timestamp On Batch Retry	✅	7506ms
Deduplication.No Duplicate Events In Batch	✅	1501ms
Deduplication.Different Events Have Different Uuids	✅	1505ms
Compression.Sends Gzip When Enabled	✅	1506ms
Batch Format.Uses Proper Batch Structure	✅	1504ms
Batch Format.Flush With No Events Sends Nothing	✅	1004ms
Batch Format.Multiple Events Batched Together	✅	1503ms
Error Handling.Does Not Retry On 403	✅	3508ms
Error Handling.Does Not Retry On 413	✅	3505ms
Error Handling.Retries On 408	✅	7511ms

Feature_Flags Tests

✅ 1/1 tests passed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	✅	512ms

[dustinbyrne]

One minor comment + greptile review looks legit