"Is start_date_time in TDIS always supposed to be defined using the "%m/%d/%Y" format?"

[javgs-bd]

I have used the following tdis definition

tdis = flopy.mf6.ModflowTdis(
sim,
time_units = "days",
start_date_time = "'31/12/2002",
nper = nper,
perioddata = period_data,
filename = 'mymodel.tdis'
)

However executing gwf.modeltime afterwards throws:
ValueError: time data '31/12/2002' does not match format '%m/%d/%Y'

Is this a bug?
If this is a standard format, should this error be thrown in the tdis creation pkg?

Regards,
Javier

[emorway-usgs]

What happens if you set start_date_time to "12/31/2002" instead of what you have currently (day/month/year: "31/12/2002")?

[javgs-bd]

Thanks for the quick reply @emorway-usgs,
Setting start_date_time to "12/31/2002" in the TDIS package results in no error thrown on calling gwf.modeltime

[wpbonelli]

We check a few different orderings but don't currently support day/month/year. if this is common enough we probably should?

[javgs-bd]

Thanks @wpbonelli. If I'm not mistaken %d/%m/%Y it is a pretty common format At least in the Americas (except the US) and Europe.
But regardless if flopy will support that format in the future, I wonder if "%m/%d/%Y" will be the standard for modeltime objects, then it would be convenient to have an error check when creating the Tdis package.

[jlarsen-usgs]

@javgs-bd

Interpreting date formats without additional context is one of the tougher things to do.

e.g., 01/02/2025

is this January 2nd or February 1st? It's ambiguous. If you have any ideas on how to resolve the ambiguity, it'd be great to add support for the %d/%m/%Y format to ModelTime.

The %m/%d/%Y format support was added as a supported type to ModelTime, because it was previously supported as the input format for the start_datetime parameter in the modflow 2005/nwt support. The input documentation for modflow-6 gives a suggested format that we also support: ISO 8601.

Here are examples of all currently supported time formats:

Supported formats for string objects representing November 12th, 2024
        are as follows:

        '11/12/2024'
        '11-12-2024'
        '2024/11/12'
        '2024-11-12'

        Time can also be represented in the string object. Example formats
        representing 2:31 pm on November 12th, 2024 are as follows:

        '2024-11-12T14:31:00'
        '2024/11/12T14:31:00'
        '11-12-2024t14:31:00'
        '11/12/2024t14:31:00'
        '2024-11-12 14:31:00'
        '2024/11/12 14:31:00'
        '11-12-2024 14:31:00'
        '11/12/2024 14:31:00'

[mwtoews]

Outside the US, MDY is uncommon. DMY is more common across different countries. More info here: https://en.wikipedia.org/wiki/List_of_date_formats_by_country

Pandas is a decent tool to deal with the complex topic of different datetime formats, see guess_datetime_format() and to_datetime().