exodusii

A Python interface for reading, writing, comparing, querying, and spatially reducing Exodus II finite-element databases.

Requires Python ≥ 3.13 and netCDF4.

Installation

python -m pip install -e .

Run tests:

cd /path/to/exodusii
pytest tests/api/ tests/mesh/ tests/core/ tests/cli/ tests/io/ tests/compat/ tests/test_attributes.py

Reading a database

from exodusii import ExodusFile

with ExodusFile.open("results.exo") as exo:
    print(exo.title)
    print(exo.dimension)  # 1, 2, or 3
    print(exo.node_count)
    print(exo.element_count)
    print(exo.times())

    coords = exo.coordinates()  # (n_nodes, dim)
    temp = exo.values("TEMP", on="node", time="last")
    energy = exo.values("ENERGY", on="element", block_id=1, time="last")
    ke = exo.values("KE", on="global")  # full time history

    print(exo.element_block_ids())
    print(exo.variable_names("node"))
    print(exo.variable_names("element"))

Time selectors: "first", "last", an int (0-based index), or a float (nearest physical time).

Writing a database

import numpy as np
from exodusii import ExodusWriter

coords = np.array([[0, 0], [1, 0], [1, 1], [0, 1]], dtype=float)

with ExodusWriter.create("out.exo") as w:
    # Declare all counts upfront — this cannot change after initialize()
    w.initialize("my mesh", dimension=2, node_count=4, element_count=1, element_blocks=1)
    w.write_coordinates(coords)
    w.define_element_block(10, "quad", [[1, 2, 3, 4]])

    w.define_global_variables(["TOTAL_ENERGY"])
    w.define_node_variables(["TEMP"])
    w.define_element_variables(["STRESS"])

    w.write_time(0.0)
    w.write_global_values([0.0])
    w.write_node_values("TEMP", [100.0, 200.0, 300.0, 400.0])
    w.write_element_values("STRESS", [42.0], block_id=10)

Parallel / decomposed Exodus files

from exodusii import ParallelExodusFile

with ParallelExodusFile.open("mesh.e.4.0", "mesh.e.4.1", "mesh.e.4.2", "mesh.e.4.3") as exo:
    print(exo.node_count)  # global node count
    coords = exo.coordinates()  # assembled from all pieces
    temp = exo.values("TEMP", on="node", time="last")

# Join all pieces into a single serial file
with ParallelExodusFile.open(*files) as exo:
    exo.write("joined.exo")

Aggregation uses the per-file node_num_map / elem_num_map. If a map is absent a UserWarning is emitted and a sequential fallback is used (only correct for non-overlapping partitions).

Fast global reads from decomposed files

Global scalar variables are fully present in every component file. Use the --piece CLI flag to read one small piece directly and avoid opening the full joined (potentially multi-GB) database:

python -m exodusii stats  run.exo.96.00 --select g/MAT_MASS_1 --piece 0
python -m exodusii query  run.exo.96.00 --select g/MASSDELETED --time last --piece 0

Region-masked statistics and mass

Compute statistics of a field variable restricted to a geometric region, with an optional field-threshold predicate:

from exodusii import ExodusFile
from exodusii.mesh import Cylinder

with ExodusFile.open("run.exo") as exo:
    cyl = Cylinder([0, 0, 0], [0.05, 0, 0], radius=0.013)

    # Field statistics inside a cylinder, filtered by a field predicate
    r = exo.region_stats(
        "YIELD_STRESS_2",
        block_id=3,
        region=cyl,
        where="EQPS_2 > 1.0",  # VARNAME OP VALUE only
        reduce=["mean", "max", "count"],
        time="last",
        symmetry_factor=4.0,  # applied to sum/count; NOT mean/max
    )
    print(r.stats["mean"], r.count_selected)

    # Material mass inside a region
    result = exo.region_mass(
        block_id=3,
        region=cyl,
        density_name="DENSITY",
        volfrac_name="VOLFRC_2",  # optional volume fraction
        time="last",
        symmetry_factor=4.0,
    )
    print(result.mass)  # = 4 * sum(|vol| * density * volfrac)

Available reducers: mean, max, min, sum, count, std. Symmetry factor scales only the extensive reducers (sum, count, mass).

CLI:

python -m exodusii region-stats run.exo \
  --select e/YIELD_STRESS_2 \
  --cylinder 0 0 0 0.05 0 0 0.013 \
  --where "EQPS_2 > 1.0" \
  --reduce mean,max,count \
  --time last --block 3 --symmetry 4

Region flags: --cylinder, --sphere, --circle, --rectangle.

Exodiff-style comparison

from exodusii import diff, DiffOptions, Tolerance, ToleranceMode

result = diff("gold.exo", "test.exo")
if not result:
    for vd in result.variable_diffs:
        print(vd.entity, vd.name, vd.max_delta)

# Custom tolerances
opts = DiffOptions(
    default_tolerance=Tolerance(ToleranceMode.ABSOLUTE, 1e-8),
    variable_tolerances={"PRESSURE": Tolerance(ToleranceMode.COMBINED, 1e-5)},
    exclude=frozenset({"TIME"}),
)
result = diff("gold.exo", "test.exo", opts)

# Coordinate-based mesh matching (different node/element ordering)
opts = DiffOptions(coordinate_matching=True, matching_tolerance=1e-8)
result = diff("gold.exo", "reordered.exo", opts)

Tolerance modes mirror SEACAS exodiff: relative, absolute, combined, ignore, eigenrel, eigenabs, eigencom, ulps_float, ulps_double.

TimeSelection controls which steps are compared and whether file-2 values are interpolated to file-1 time points.

python -m exodusii diff gold.exo test.exo
python -m exodusii diff --absolute -t 1e-8 gold.exo test.exo
python -m exodusii diff --start LAST gold.exo test.exo
python -m exodusii diff --match-coordinates gold.exo reordered.exo
python -m exodusii diff --format json --terse gold.exo test.exo

Exit codes: 0 same, 1 error, 2 different.

Command (control) files

A diff can be driven by a command file on disk. Two formats are supported; exodusii.read_command_file() (and the CLI -f/--command-file) auto-detect which one a file uses. Explicit CLI flags override values from the file.

YAML (preferred, modern)

A structured, self-documenting format with full feature parity with the SEACAS exodiff command file:

# opts.yaml
tolerances:
  default:    {mode: relative, value: 1.0e-6, floor: 1.0e-12}
  coordinate: {mode: absolute, value: 1.0e-8}
  time:       {mode: relative, value: 1.0e-6, floor: 1.0e-15}
  categories:                         # per-category default tolerances
    nodal:  {mode: absolute, value: 1.0e-7}
  variables:                          # per-variable overrides (highest priority)
    DISPLX: {mode: relative, value: 1.0e-9}
variables:
  ignore_case: true
  exclude: [VELZ]
  include:                            # per-category include lists
    nodal:  [DISPLX, DISPLY]
    global: all                       # 'all' => compare all variables
coordinates:  {compare: true}
attributes:   {compare: true}
mesh_matching: {enabled: false, tolerance: 1.0e-6, require_unique: true}
time:
  start: 1
  stop: -1
  increment: 1
  step_offset: 0
  exclude_steps: []
  interpolate: false
report: {show_all: false}

Any tolerance may be an explicit mapping, a shorthand string ("absolute 1e-8" / "1e-6"), or a bare number.

python -m exodusii diff -f opts.yaml gold.exo test.exo

import exodusii

res = exodusii.read_command_file("opts.yaml")  # -> CommandFileResult
result = exodusii.diff("gold.exo", "test.exo", res.options)

Emit a YAML command file from a DiffOptions (full/explicit; round-trips):

opts = exodusii.DiffOptions(...)
opts.to_yaml("opts.yaml")  # write to a file
print(opts.to_yaml())  # or get the string

# Emit the effective options (command file + CLI flags) and exit, no compare
python -m exodusii diff --absolute -t 1e-8 --emit-options opts.yaml gold.exo test.exo
python -m exodusii diff --emit-options - gold.exo test.exo   # to stdout

SEACAS exodiff text (legacy, backward compatible)

The original whitespace-delimited exodiff command-file grammar is also accepted (auto-detected):

# cmds.txt  (SEACAS exodiff command-file grammar)
DEFAULT TOLERANCE relative 1e-6 floor 1e-12
COORDINATES absolute 1e-8
NODAL VARIABLES absolute 1e-7
	DISPLX relative 1e-9      # per-variable override
	!VELZ                     # exclude
GLOBAL VARIABLES (all) relative 1e-4

python -m exodusii diff -f cmds.txt gold.exo test.exo

Directives: DEFAULT TOLERANCE, COORDINATES, TIME STEPS, FINAL TIME TOLERANCE, per-category <GLOBAL|NODAL|ELEMENT|NODESET|SIDESET|EDGEBLOCK| FACEBLOCK> VARIABLES blocks (with (all), per-variable tolerances, and !name exclusions), ELEMENT ATTRIBUTES, STEP OFFSET, EXCLUDE TIMES, INTERPOLATE, APPLY MATCHING/NODESET MATCH/SIDESET MATCH, and IGNORE CASE/CASE SENSITIVE. Keywords are case-insensitive and abbreviable. A category block that lists specific names (without (all)) restricts the comparison to those names for that category. Accepted-but-inert directives (e.g. PEDANTIC, CALCULATE NORMS) are reported via CommandFileResult.warnings.

The reader classes (YamlCommandFileReader, ExodiffCommandFileReader) share the abstract CommandFileReader base; command_file_reader(path) is the format-detecting factory (YAML preferred).

Query and stats CLI

# Inspect a database
python -m exodusii inspect  mesh.exo
python -m exodusii variables mesh.exo
python -m exodusii blocks   mesh.exo
python -m exodusii times    mesh.exo

# Query result variables (JSON output)
python -m exodusii query mesh.exo --select g/TOTAL_ENERGY
python -m exodusii query mesh.exo --select n/TEMP --time last --limit 10
python -m exodusii query mesh.exo --select e/ENERGY --time step:5

# Compact numeric summaries
python -m exodusii stats mesh.exo --select n/TEMP --time last
python -m exodusii stats mesh.exo --select e/ENERGY --time last --by-block

Variable selector format: ENTITY/NAME — e.g. g/TOTAL_ENERGY, n/TEMP, e/ENERGY, ns/FLUX, ss/PRESSURE.

Python query API

from exodusii import ExodusFile, query, print_query

with ExodusFile.open("mesh.exo") as exo:
    result = query(exo, "n/TEMP", "e/ENERGY", time="last")
    print(result.names)
    print(result.data[:5])
    print_query(exo, "g/TM_STEP")

Mesh geometry helpers

from exodusii.mesh import entity_centers, element_volumes, bounding_box
from exodusii.mesh import Cylinder, Sphere, Circle, Rectangle

with ExodusFile.open("run.exo") as exo:
    coords = exo.coordinates()
    conn = exo.element_connectivity(block_id=1, zero_based=True)

# Element centroids — feed to region.contains() to select elements
centers = entity_centers(conn, coords)

# Per-element volumes/areas
vols = element_volumes("hex8", conn, coords)

# Bounding box
lo, hi = bounding_box(coords)

# Region predicates
cyl = Cylinder([0, 0, 0], [0.05, 0, 0], radius=0.013)
mask = cyl.contains(centers)  # boolean ndarray

Supported element types: quad4, hex8, tri3, tet4, wedge6.

Agent CLI (self-learning)

# Static capability reference (no file required)
python -m exodusii learn capabilities overview
python -m exodusii learn capabilities region_reduce
python -m exodusii learn capabilities python_api.writer

# Skills (self-contained workflow guides)
python -m exodusii learn skills list
python -m exodusii learn skills exodusii-region-reduce
python -m exodusii learn skills exodusii-geometry

Package layout

exodusii/
├── api/             modern API (ExodusFile, ExodusWriter, ParallelExodusFile,
│                    diff, query, region_reduce, lineout, copy)
├── core/            domain model (Entity, Block, Tolerance, errors, schema)
├── io/              NetCDF backend (Protocol + netCDF4 implementation)
├── mesh/            geometry (elements, regions, entity_centers, element_volumes)
├── compat/          legacy ExodusIIFile / put_*/get_* API
├── cli/             JSON-oriented CLI (main.py dispatch + one file per subcommand, exodiff.py, exoread, learn)
└── data/            capabilities.json, skills.json

Legacy API (compatibility)

The historical put_* / get_* API from the original exodusii library is preserved for downstream code that has not yet migrated:

import exodusii

# Read
with exodusii.File("mesh.exo") as exo:
    times = exo.get_times()
    temp = exo.get_node_variable_values("TEMP", time_step=-1)

# Write
with exodusii.File("out.exo", mode="w") as exo:
    exo.put_init("title", 2, 4, 1, 1, 0, 0)
    exo.put_coords(coords)
    exo.put_element_block(10, "quad", 1, 4)
    exo.put_element_conn(10, [[1, 2, 3, 4]])

# Globals only
exodusii.write_globals({"energy": values}, times, filename="globals.exo")

New code should use the modern API (ExodusFile, ExodusWriter, ParallelExodusFile). The compatibility layer is fully tested and maintained but will not receive new features.