How to modify GRIB content during loading

See also: Iris-grib Load and Save API.

Here is a basic example of how you can modify the GRIB messages being loaded, and how to turn those modified messages into Iris cubes.

>>> import iris
>>> from iris.cube import CubeList
>>> from iris_grib import GribMessage, load_pairs_from_fields
>>>
>>> def adjust_message(msg: GribMessage) -> GribMessage:
...     # Advance all time steps by 1 hour.
...     if msg.sections[0]["editionNumber"] == 2:
...         s1 = msg.sections[1]
...         s1["hour"] += 1
...         s4 = msg.sections[4]
...         s4["hourOfEndOfOverallTimeInterval"] += 1
...     return msg

>>> original = iris.load_cube(filename)
>>> fields = GribMessage.messages_from_filename(filename)
>>> fields = (adjust_message(msg) for msg in fields)
>>> cubes = CubeList(cube for cube, _ in load_pairs_from_fields(fields))
>>> modified = cubes.combine_cube()

Compare the final 5 time steps of the original and modified cubes:

>>> print(original.coord("time").points[-5:])
[1084524. 1093236. 1101936. 1110636. 1119336.]
>>> print(modified.coord("time").points[-5:])
[1084525. 1093237. 1101937. 1110637. 1119337.]