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What the comparison actually asks
Consider this pattern:
end = datetime.strptime(RUNTIME.free_window_end, "%Y-%m-%d")
return datetime.now() <= endWith the input "2026-08-20", strptime returns a datetime at midnight on August 20. Python’s documentation explains that components not supplied to strptime come from the default 1900-01-01T00:00:00.000; for this format, the date is supplied but the time remains midnight. That is documented behavior, not a parser error. Python datetime documentation
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datetime.now() returns the current local date and time when called without a timezone. So at 09:00 on August 20, the code compares 09:00 with 00:00 on that same date. The comparison is false. The <= operator is doing what it says; the right-hand value represents the start of the date, while the likely requirement is to include the entire date.
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A calendar date and a precise instant are different contracts. Choose the one the configuration is intended to express before changing the comparison.
#1 Best Overall
| Policy | Meaning of the configured value | Appropriate comparison | Boundary to test |
|---|---|---|---|
| Inclusive calendar date | The entire named date is valid in a specified timezone. | Compare the current date in that timezone with the configured date. | Valid late on the final date; invalid when the next date begins. |
| Exact instant | Validity ends at a particular time and timezone or offset. | Compare timezone-aware datetimes representing the intended instants. | Test immediately before, at, and after the deadline. |
| Exclusive next-date boundary | Validity ends at the start of the day after the final included date. | Compare the current instant with that explicitly defined boundary. | Test immediately before and at the boundary. |
Make a whole calendar date inclusive
If the setting is a date such as 2026-08-20, keep it as a date and compare it with today in the timezone that defines the policy:
from datetime import date, datetime
from zoneinfo import ZoneInfo
policy_tz = ZoneInfo("America/New_York")
end_date = date.fromisoformat(RUNTIME.free_window_end)
today = datetime.now(policy_tz).date()
return today <= end_dateThis expresses “valid through the configured date” directly. Replace the example timezone with the one the application’s policy actually uses; the correct choice depends on what “today” means to the product. If the policy is intentionally based on the server’s local calendar, use that local calendar consistently instead.
Alternatively, if the existing code has already parsed a datetime and the contract is definitely date-only, compare the date parts:
return datetime.now().date() <= end.date()This short form uses the machine’s local date on the left. It is suitable only when that local calendar is the intended policy timezone. Converting both values to dates is not a general fix for expiration logic: it discards time-of-day information.
Keep an exact deadline as a timezone-aware datetime
If the rule says “until 17:00 UTC” or names another precise instant, store that instant with an explicit timezone or offset. For a UTC deadline, compare aware values:
from datetime import datetime, timezone
end = datetime.fromisoformat(RUNTIME.free_window_end)
now = datetime.now(timezone.utc)
return now <= endThis assumes the configured ISO datetime includes a UTC offset, such as +00:00. If it does not, define how the value should be interpreted rather than silently treating it as UTC. Python’s datetime.now() without a timezone is local and naive; datetime.now(timezone.utc) is aware and represents UTC. Ordering comparisons between a naive and an aware datetime raise TypeError. Python datetime documentation
Local naive datetimes are not inherently wrong when both the stored events and current time are intentionally expressed in the same local-time convention. In a Python issue discussion on January 24, 2022, Python committer Paul Ganssle noted: “Of course, if you are consuming a bunch of event dates stored in local time and you want to compare them to the current time, then datetime.now() would be appropriate.” Python issue discussion
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Use the next day only when the boundary is explicit
Another way to represent an inclusive date is an exclusive boundary at midnight on the following date: the interval includes times before that boundary, but not the boundary itself. This can make interval checks clear, provided the application defines the timezone and constructs the next local midnight according to that timezone’s calendar rules.
Do not assume that every local day is exactly 24 hours. Daylight-saving transitions can change the elapsed time between consecutive local midnights. Python documents cases where local times are ambiguous or repeated; these rules matter when constructing local-time boundaries. PEP 495 – Local Time Disambiguation
Test the boundary, not just an ordinary date
Make the current time controllable in tests so the cases verify the contract rather than depending on the clock when the test runs. For an inclusive calendar-date policy ending on August 20, check:
- A moment shortly after midnight on August 20: valid.
- A late moment on August 20: valid.
- A moment just after the next date begins: invalid.
- A clearly earlier valid date: valid.
Name tests to make the policy visible, for example, test_end_date_includes_late_time_on_final_day. For an exact timestamp policy, test immediately before, exactly at, and immediately after the deadline, including conversions from any supported timezone. The source article describes these boundary cases as a safeguard. The reported incident and code example
What is known about the reported 12-hour block
The author of the linked DEV Community article reports that this comparison blocked requests for 12 hours. The Python behavior explains how a date parsed at midnight can make an intended inclusive end date expire as it begins, but the incident duration and operational account are the author’s report; the cited Python documentation does not independently confirm that production incident.
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