f90nml

library1.5pypypi✓ verified 85d ago

A Python module for reading and writing Fortran 90 namelist files. Current version is 1.5 with irregular release cadence. Supports parsing, modifying, and writing namelist files, preserving structure and comments.

serialization data

pip install f90nml

github ↗package ↗

INSTALL

IMPORT

SIG · F90NML

f90nml

serializationpythonv1.5

Install

1.5s avg

Import

19ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v1.5.0 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.020s · 18.2MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.5s · import 0.018s · 19MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

f90nml

✓ import f90nml

✗ from f90nml import parse

Wrong because f90nml uses a module-level API; direct import of parse may be unconventional.

Basic usage: read, modify, write namelist files.

import f90nml import os # Read a namelist file nml = f90nml.read('path/to/namelist') # Access a variable print(nml['namelist_name']['variable_name']) # Write back nml.write('output.nml') # Create from dict data = {'namelist': {'var1': 1.0, 'var2': 2}} nml = f90nml.Namelist(data) nml.write('new.nml')

Debug

Known issues

deprecatedThe write() method with a file path is deprecated in favor of using open() and write() with a file object.

fix

Use: with open('file.nml', 'w') as f: nml.write(f)

affects: >=1.4

breakingDuplicate keys behavior changed: in version 1.4, duplicate keys are now stored as Cogroup objects, not lists. Code expecting plain lists will break.

fix

Handle duplicate keys via f90nml.Cogroup or use nml.todict() with dups=True to get list representation.

affects: >=1.4

gotchaEmpty lists in namelist are formatted as comma-delimited blanks (e.g., ',,') instead of an empty line. This can cause confusion when re-parsing.

fix

Use custom formatting or work with string representation if needed.

affects: >=1.4.1

gotchaThe parser treats unquoted strings case-sensitively. Fortran normally treats them case-insensitively, leading to unexpected mismatches.

fix

Manually convert string values to lowercase/uppercase as needed.

affects: all

Errors

Common errors & fixes

AttributeError: module 'f90nml' has no attribute 'Namelist'

Typo in class name: correct is 'Namelist' with capital 'N'.

fix

Use: from f90nml import Namelist or f90nml.Namelist

TypeError: write() argument must be str, not _io.TextIOWrapper

Passing a file object to write() without specifiying mode 'w' or using deprecated string path.

fix

Use: with open('file.nml', 'w') as f: nml.write(f)

ValueError: Invalid key: 'mykey' - key must be a string

Keys passed to Namelist constructor or assignments must be strings.

fix

Ensure all namelist group and variable names are strings.

AttributeError: 'Cogroup' object has no attribute 'append'

Cogroup does not support append; use list-like indexing or extend.

fix

Use: nml['group']['key'].extend([value]) or nml['group']['key'] = f90nml.Cogroup([value1, value2])

Upgrade

Version history

1.5latest on PyPI · released Oct 7, 2025

Audit

Dependencies

No dependency data recorded yet.

Agent activity

18 hits · last 30 days

node

Resources

githubhttps://github.com/marshallward/f90nml ↗

packagehttps://pypi.org/project/f90nml/ ↗