isocalendar0

isocalendar0 is a convention used in some date-time libraries to extract ISO calendar components from a date using zero-based indexing for weeks and weekdays. It is not part of the ISO 8601 standard and is not universally implemented; it exists mainly in contexts where zero-based values align with array indices or specific numerical schemes.

In isocalendar0, the function returns a triple consisting of year, week, and weekday. The week number starts at 0 (ranging from 0 to 53), and the weekday is also zero-based, typically with Monday mapped to 0 and Sunday to 6. This contrasts with the standard ISO approach, where week numbers start at 1 and weekdays often start at 1 (Monday) or use a separate convention.

Relationship to standard isocalendar and ISO 8601: the conventional isocalendar used in Python and many libraries follows ISO 8601, where weeks are numbered starting at 1 and weekdays are numbered 1 through 7. Because of these differences, software that interoperates with both schemes must perform explicit conversions or documentation clarifications to avoid off-by-one errors.

Availability and usage: isocalendar0 is implemented only in a minority of libraries or as a user-defined utility; it is not a canonical naming in the broader ecosystem. When used, clear documentation is essential to prevent misinterpretation and to ensure consistent integration with other date-time components.

Example: for the date 2023-01-02, which is a Monday in the first ISO week of 2023, isocalendar0 would yield (2023, 0, 0) under a Monday=0, weekday=0 convention. See also isocalendar, ISO week date, and ISO 8601.