Automatic download functionality

[Arjanvw]

Describe the bug

The function nlmod.get_ds() tries to download the modflow executable through to_model_ds > set_ds_attrs > get_exe_path > get_bin_directory > download_mfbinaries. This results in an error URLError: <urlopen error [WinError 10054] De externe host heeft een verbinding verbroken>.

I want to construct a ds for modelling and don't need the mfbinaries, there seem te be no option to switch the download option off.

Expected behavior

An option to turn off the automatic download from nlmod.get_ds()

Code to reproduce

# make a dataset with nlmod
ds = nlmod.get_ds(
    model_name="model",
    model_ws="ws",
    extent=(0,100,0,100),
    layer=range(3),
    delr=10,
    delc=10,
    xorigin=0,
    yorigin=0,
)

Package and Python version

Python version : 3.12.12
NumPy version : 2.3.5
Xarray version : 2025.10.1
Matplotlib version : 3.10.7
Flopy version : 3.9.5

nlmod version : 0.10.0
hydropandas version: 0.18.0

Additional context

Add any other context about the problem here. If applicable, add screenshots to help explain your problem.

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[dbrakenhoff]

Alright, I've submitted a fix here: #533

This should allow you to add a download_exe=False to nlmod.get_ds()

A bit of background:

nlmod, by default, will search for the exe in the following locations in this order:

• the current directory (i.e. the directory the python file is in)
• %LOCALAPPDATA%\flopy
• <nlmod install directory, e.g. site-packages>/nlmod/bin/ (note that depending on the install type, normal or editable, this is in your python env or in your local nlmod folder>

So adding your mf6.exe file to one of these locations should also have prevented the download from being attempted. Can you specify where you placed your mf6.exe file? You can check whether nlmod is able to find the exe with nlmod.util.get_exe_path("mf6", download_if_not_found=False).

If nlmod cannot find it, it will attempt to download it. The underlying functions allowed disabling of the download if the exe was not found, but this was not exposed in the higher level functions.

The idea behind the auto-download function, and some of the associated arguments was that nlmod allows you to specify a version_tag associated with a modflow release. Unfortunately this is not the modflow 6 version itself, but another tag that specifies the release of a bunch of modflow binaries. Providing this version_tag guarantees that your model will be run with the same version of the binary each time. Which is kind of cool, but also adds a lot of complicated logic to this part of the nlmod code.