Troubleshooting

Troubleshooting

ImportError: pyfdstools.paraview requires optional dependencies...

ImportError: pyfdstools.paraview requires optional dependencies which are
not installed (No module named 'evtk'). Install them with
'pip install pyfdstools[paraview]'.

The ParaView export and VTKHDF submodules wrap large third party libraries which are not core dependencies. Install the extra the message names:

python -m pip install "pyfdstools[paraview]"
python -m pip install "pyfdstools[vtk]"
python -m pip install "pyfdstools[all]"

Importing pyfdstools itself never requires them, so this only appears when you reach for a name they provide.

AttributeError: module pyfdstools has no attribute ...

The name does not exist. If the message goes on to say that an optional submodule could not be imported, the name may be one of theirs — install the extra as above. Otherwise check the spelling against the API Reference.

Warning did not find a 2-D slice of ... on axis ... at value ...

query2dAxisValue returned (None, None) because the case has no slice in that plane. It prints the planes that do exist:

Available slices of qty TEMPERATURE:
	Axis	Value
	1	2.5500
	-1	-1.0000

Three common causes:

• Wrong plane. Pick one from the list.
• A coordinate that is close but not equal. The match tolerance defaults to 1e-8. Loosen it: atol=1e-3.
• The slice is 3-D. An axis of -1 means that file covers a volume. Use readSLCF3Ddata(chid, workingDir, qty, axis=..., value=...) instead, which extracts a plane from it.

No 3D slice data found for qty ...

readSLCF3Ddata returned (False, False, False, False). It prints every quantity the case wrote; check the spelling — FDS quantity names are exact, including spaces ('WALL TEMPERATURE', not 'Wall Temperature').

Guard for it:

grid, values, times, units = fds.readSLCF3Ddata(chid, workingDir, qty)
if grid is False:
    raise SystemExit('%s was not written by this case' % (qty))

ValueError: axis must be one of -3, -2, -1, 1, 2, or 3

queryBndf takes the axis as a scalar, not a list, and it may be signed:

fds.queryBndf(workingDir, chid, fdsFilePath, ['WALL TEMPERATURE'], -2, 4.4)
#                                            ^ list              ^ scalar

where fdsFilePath is the path to the case's .fds input file.

The sign selects which side of the surface to read. See Boundary Data.

FileNotFoundError: No smokeview (.smv) file for chid ... was found

Either the chid is wrong, or the working directory is. Check what is actually there:

import os
import zipfile

if workingDir.endswith('.zip'):
    print(zipfile.ZipFile(workingDir).namelist())
else:
    print(os.listdir(workingDir))

If the input file sets RESULTS_DIR on &DUMP, point pyfdstools at the directory holding the input file, not the output subdirectory; it follows RESULTS_DIR itself.

FileNotFoundError: No xyz file for chid ... Add WRITE_XYZ=.TRUE.

Plot3D output carries no coordinates of its own, so readPlot3Ddata needs the .xyz files. Re-run with:

&DUMP DT_PL3D=30., WRITE_XYZ=.TRUE. /

Slice and boundary readers do not need this — they take the grid from the smokeview file.

FileNotFoundError: No csv file matching '...' for chid ...

The case did not write that output. _devc.csv only exists if the case had &DEVC lines; _ctrl.csv only if it had &CTRL.

Everything comes back as NaN

Cells outside every mesh are NaN by design. If the whole array is NaN:

• The plane may lie outside the domain. Check the mesh extents:

  smv = fds.parseSMVFile(fds.getSmvFile(workingDir, chid))
  for trnx, trny, trnz in smv['grids']:
      print(trnx[[0, -1], 1], trny[[0, -1], 1], trnz[[0, -1], 1])

• The run may have produced no output at the requested time.

Use np.nanmax, np.nanmean and friends rather than their plain counterparts throughout.

The values look wrong by a constant

If you are comparing against numbers from an earlier pyfdstools release, several calculations were corrected in v0.0.24 and now give different answers:

Routine	Was
slice time averaging with time and dt	summed N frames and divided by N−1
astFromGhf	mixed Celsius and Kelvin; a zero flux did not return the gauge temperature
getTwoZone	reversed an ascending profile, reporting an upper layer cooler than the lower
readPlot3Ddata	read one mesh's .q file for every mesh

Re-run the calculation rather than reconciling against the old numbers.

ValueError: setting an array element with a sequence while parsing

Fixed in v0.0.24. Stretched meshes (&TRNX, &TRNY, &TRNZ) insert extra lines into the smokeview grid records, which earlier releases could not parse. Upgrade.

AttributeError: module 'numpy' has no attribute 'trapz'

Fixed in v0.0.24. np.trapz was removed in numpy 2.0. Upgrade pyfdstools, or pin numpy<2.

Reading is slow

• Reading from a zip archive. Compressed members cannot be seeked into, so a large slice file is decompressed from the start on every read. Extract the case first if you are querying it repeatedly.
• Reading every frame when you need one. Pass time and dt.
• Assembling a volume to take a plane out of it. Pass axis and value to readSLCF3Ddata.
• Re-scanning timestamps. Pass saveTimesFile=True to cache them in a csv beside each slice file.

No figure appears

On a machine with no display, matplotlib needs a non-interactive backend:

import matplotlib
matplotlib.use('Agg')
import matplotlib.pyplot as plt

or set MPLBACKEND=Agg. fig.savefig still works; plt.show() becomes a no-op.

A plot's colors jump between frames

Fix the color scale. Without qnty_mn and qnty_mx, each frame is scaled to its own range:

fds.plotSlice(data['x'], data['z'], data['datas'][:, :, i], axis,
              qnty_mn=20, qnty_mx=1000)

Smokeview does not show a file I wrote

Smokeview only displays files a record in the smokeview file names. The slcfsTimeAverage and bndfsTimeAverage routines write a new smokeview file for you and return its path — open that one, not the original. If you wrote the output file yourself, use writeSliceToSmv or buildBndfSmvLine to add the record.

&GEOM boundary element files are the exception: appendNewBeFileToSMV is an unimplemented stub, so the BNDE record has to be added by hand.

An input file round-trips with quotes around a number

The parameter is not in fdsLineTypes, so it is treated as a string. Add it to the relevant getXXXXtypes method in pyfdstools/fdsTypes.py:

surfTypes['MY_PARAMETER'] = 'float'

and please open a pull request.

Iterating a namelist group hits an integer

Multi-entry groups carry a bookkeeping 'unknownCounter' entry:

for key in model.meshes:
    if key == 'unknownCounter':
        continue
    ...

Still stuck

Open an issue at https://github.com/johodges/pyfdstools/issues with the pyfdstools version (fds.__version__), the FDS version that produced the results, and the full traceback.