inifix

inifix is a small Python library offering a load/dump interface similar to standard library modules json or tomllib (together with tomli_w) for ini configuration files in the style of Pluto and Idefix.

While its primary goal is to follow Idefix's 'ini' format specification, it supports a small superset of it.

The key differences are:

• inifix supports section-free definitions. This means configuration files from FARGO 3D are also supported.
• in inifix, strings can be escaped using ' or ". This allows to have whitespaces in string values and to force string type decoding where numeric and boolean types would work.

In rare cases where Idefix's 'ini' format doesn't match Pluto's, inifix takes the path of least resistance to support both.

Known differences are:

• Idefix allows booleans to be written as yes and no, as so does inifix, but these are not valid in Pluto (as of version 4.4). Note that in contrast to Idefix, which is truly case-insensitive about these special strings, inifix (from version 5.0.0) only parse a restricted set of unescaped strings as booleans, like true, TRUE, True, yes, Yes and YES, but TruE or yES for instance will be parsed as strings.
• Idefix allows integers to be written using decimal notation (e.g. 1.0 or 1e3). This creates some ambiguity when deserializing such strings, as the expected type (int or float) cannot be unambiguously guessed. By default, inifix (from version 5.0) will parse these as floats, allowing for 1-to-1 roundtrips. Idefix (as of version 2.1) is also resilient against integers written as decimal, so inifix will not break any working inifile by a load/patch/dump routine. See Reading Options for more.

File format specifications details

# My awesome experiment
[Grid]
x   1 2 u 10    # a comment
y   4 5 l 100
[Time Integrator]
CFL  1e-3
tstop 1E3

{
    "Grid": {
        "x": [1, 2, "u", 10],
        "y": [4, 5, "l", 100]
    },
    "Time Integrator": {
        "CFL": 0.001,
        "tstop": 1000.0
    }
}

mode   fargo

# Time integrator
CFL    1e-3
tstop  1e3

{
    "mode": "fargo",
    "CFL": 0.001,
    "tstop": 1000.0
}

Installation

python -m pip install inifix

Usage

The public API mimics that of Python's standard library json, and consists in four main functions:

• inifix.load and inifix.dump read from and write to files respectively
• inifix.loads reads from a str and returns a dict, while inifix.dumps does the reverse operation.

Reading data

inifix.load reads from a file and returns a dict

import inifix

with open("pluto.ini", "rb") as fh:
    conf = inifix.load(fh)

# or equivalently
conf = inifix.load("pluto.ini")

Files are assumed to be encoded as UTF-8.

Reading options

inifix.load and inifix.loads accept an optional boolean flag parse_scalars_as_lists (new in inifix v4.0.0), that is useful to simplify handling unknown data: all values can be safely treated as arrays, and iterated over, even in the presence of scalar strings. For illustration

>>> import inifix
>>> from pprint import pprint
>>> pprint(inifix.load("example.ini"))
{'Grid': {'x': [1, 2, 'u', 10], 'y': [4, 5, 'l', 100]},
 'Time Integrator': {'CFL': 0.001, 'tstop': 1000.0}}
>>> pprint(inifix.load("example.ini", parse_scalars_as_lists=True))
{'Grid': {'x': [1, 2, 'u', 10], 'y': [4, 5, 'l', 100]},
 'Time Integrator': {'CFL': [0.001], 'tstop': [1000.0]}}

inifix.load and inifix.loads also accept an integer_casting argument (new in inifix v5.0.0), which can be set to decide how numbers written in decimal notation which happen to have integral values (e.g. 1e2 or 30000.) should be parsed. This argument accepts two values: 'stable' (default) gives floats while 'aggressive' gives ints, matching the behavior of inifix v4.5.0.

The key difference is that the default strategy is roundtrip-stable on types, while the aggressive mode isn't:

>>> import inifix
>>> data = {'option_a': [0, 1., 2e3, 4.5]}
>>> data
{'option_a': [0, 1.0, 2000.0, 4.5]}
>>> inifix.loads(inifix.dumps(data))
{'option_a': [0, 1.0, 2000.0, 4.5]}
>>> inifix.loads(inifix.dumps(data), integer_casting='aggressive')
{'option_a': [0, 1, 2000, 4.5]}

Aggressive casting may also lead to loss of precision beyond a certain range

>>> import inifix
>>> data = {'option_b': 9_007_199_254_740_993}
>>> inifix.loads(inifix.dumps(data))
{'option_b': 9007199254740993}
>>> inifix.loads(inifix.dumps(data), integer_casting='aggressive')
{'option_b': 9007199254740992}

By default, inifix.load and inifix.loads validate input data. This step can be skipped by specifying skip_validation=True.

Writing to a file or a string

inifix.dump writes data to a file.

One typical use case is to combine inifix.load and inifix.dump to programmatically update an existing configuration file at runtime via a load/patch/dump routine.

>>> import inifix
>>> with open("pluto.ini", "rb") as fr:
...    inifix.load(fr)
>>> conf["Time"]["CFL"] = 0.1
>>> with open("pluto-mod.ini", "wb") as fw:
...    inifix.dump(conf, fw)

or, equivalently

>>> import inifix
>>> inifix.load("pluto.ini")
>>> conf["Time"]["CFL"] = 0.1
>>> inifix.dump(conf, "pluto-mod.ini")

Data will be validated against inifix's format specification at write time. Files are always encoded as UTF-8.

inifix.dumps is the same as inifix.dump except that it returns a string instead of writing to a file.

>>> import inifix
>>> data = {"option_a": 1, "option_b": True}
>>> print(inifix.dumps(data))
option_a 1
option_b True

By default, inifix.dump and inifix.dumps validate input data. This step can be skipped by specifying skip_validation=True.

Schema Validation

inifix.validate_inifile_schema can be used to validate an arbitrary dictionary as writable to an inifile, following the library's format. This will raise an exception (ValueError) if the dictionary data is invalid.

inifix.validate_inifile_schema(data)

Runtime formatting

inifix.format_string formats a string representing the contents of an ini file. See Formatting CLI for how to use this at scale.

Writing type-safe applications of inifix.load(s)

inifix.load has no built-in expectations on the type of any specific parameter; instead, all types are inferred at runtime, which allows the function to work seamlessly with arbitrary parameter files.

However, this also means that the output is not (and cannot be) type-safe. In other words, type checkers (e.g. mypy) cannot infer exact types of outputs, which is a problem in applications relying on type-checking.

A solution to this problem, which is actually not specific to inifix.load and works with any arbitrarily formed dict, is to create a pipeline around this data which implements type-checkable code, where data is also validated at runtime.

We'll illustrate this with a real-life example inspired from nonos. Say, for instance, that we only care about a couple parameters from the [Output] and [Hydro] sections of idefix.ini. Let's build a type-safe read_parameter_file function around these.

class IdefixIni:
    def __init__(self, *, Hydro, Output, **kwargs):
        self.hydro = IdefixIniHydro(**Hydro)
        self.output = IdefixIniOutput(**Output)

class IdefixIniHydro:
    def __init__(self, **kwargs):
        if "rotation" in kwargs:
            self.frame = "COROT"
            self.rotation = float(kwargs["rotation"])
        else:
            self.frame = "UNSET"
            self.rotation = 0.0

class IdefixIniOutput:
    def __init__(self, *, vtk, **kwargs):
        self.vtk = float(vtk)

def read_parameter_file(file) -> IdefixIni:
    return IdefixIni(**inifix.load(file))

ini = read_parameter_file("idefix.ini")

Type checkers can now safely assume that, ini.hydro.frame, ini.hydro.rotation and ini.output.vtk all exist and are of type str, float and float, respectively. If this assumption is not verified at runtime, a TypeError will be raised.

Note that we've used the catch-all **kwargs construct to capture optional parameters as well as any other parameters present (possibly none) that we do not care about.

CLI

Command line tools are shipped with the package to validate or format compatible inifiles.

Validation CLI

This checks that your inifiles can be loaded with inifix.load from the command line

$ inifix-validate pluto.ini
Validated pluto.ini

This CLI can also be called as python -m inifix.validate.

Formatting CLI

To format a file in place, use

$ inifix-format pluto.ini

inifix-format is guaranteed to preserve comments and to only edit (add or remove) whitespace characters.

Files are always encoded as UTF-8.

To print a diff patch to stdout instead of editing the file, use the --diff flag

$ inifix-format pluto.ini --diff

This CLI can also be called as python -m inifix.format.

By default, inifix-format also validates input data. This step can be skipped with the --skip-validation flag

pre-commit hooks

inifix-validate and inifix-format can be used as pre-commit hooks with the following configuration (add to .pre-commit-config.yaml)

  - repo: https://github.com/neutrinoceros/inifix.git
    rev: v5.0.3
    hooks:
      - id: inifix-validate

or

  - repo: https://github.com/neutrinoceros/inifix.git
    rev: v5.0.3
    hooks:
      - id: inifix-format

Note that inifix-format also validates data by default, so it is redundant to utilize both hooks. Validation and formatting may nonetheless be decoupled as

  - repo: https://github.com/neutrinoceros/inifix.git
    rev: v5.0.3
    hooks:
    - id: inifix-validate
    - id: inifix-format
+     args: [--skip-validation]

By default, both hooks target files matching the regular expression (\.ini)$. It is possible to override this expression as, e.g.,

   hooks:
   - id: inifix-format
+    files: (\.ini|\.par)$

Testing

We use the pytest framework to test inifix. The test suite can be run from the top level with a simple pytest invocation.

$ python -m pip install --requirement requirements/tests.txt
$ pytest