Casting between datatypes

This is a compendium of how ibis treats casts between various datatypes. This often follows the semantics of the underlying backend, but sometimes ibis adds some glue code in between to make things consistent between backends.

Timestamps

When casting from numeric types such as integers, decimals, and floating values, timestamps treated as the number of seconds since the epoch. So 0 is 1970-01-01 00:00:00 and 1 is 1970-01-01 00:00:01. Subsecond fractions are supported when possible. Casting to numeric types is not implemented for most backends, but should be the inverse of the above. For example, ibis.literal('1970-01-01 00:00:01').cast(int) should return 1. If the timestamp has subsecond resolution, timestamp is truncated to the second.

When casting to/from strings, the format is YYYY-MM-DD HH:MM:SS[.SSSSSSSSS]. We haven’t gotten to defining behavior with timezones in the string yet. Some backends may work, but others may not. PRs to implement this are welcomed!

Intervals

When casting to/from numeric types such as integers, decimals, and floating values, intervals are treated as the number of the particular interval. For example ibis.literal(123).cast("interval('s')") results in an interval of 123 seconds. Casting the other direction from intervals to integers is not currently supported.