Using Data Files

Table of contents

Gestalt layouts can accept external input data that gets substituted into the layout as macros. Data is provided via the --input flag and can come in several formats.

YAML

YAML is the most common input format. Provide a file with key-value pairs:

# data.yml
MOTORS: 8
ASPECT: 2.0
PADDING: 15
PREFIX: "IOC1:"

python gestalt.py --to ui --input data.yml --output screen.ui layout.yml

Values are referenced in the layout with {NAME}:

Grid: !Grid
    repeat-over: "MOTORS"
    aspect-ratio: "{ASPECT}"
    padding: "{PADDING}"

YAML data files can contain nested structures – lists and dictionaries – which are useful for driving repeat nodes:

CHANNELS:
    - { N: 1, label: "Channel 1", pv: "Ch1" }
    - { N: 2, label: "Channel 2", pv: "Ch2" }

Gestalt auto-detects YAML from .yml and .yaml file extensions. You can also specify it explicitly with --from yaml.

Inline YAML strings

For quick tests or simple data, you can pass a YAML string directly on the command line instead of creating a file:

python gestalt.py --to ui --input "{MOTORS: 4, ASPECT: 2.0}" --from str --output screen.ui layout.yml

The --from str flag tells Gestalt to parse the --input value as a YAML string rather than a file path.

JSON

JSON files work the same way as YAML. Provide a JSON file with the macros:

{
    "MOTORS": 8,
    "ASPECT": 2.0,
    "CHANNELS": [
        {"N": 1, "label": "Ch 1"},
        {"N": 2, "label": "Ch 2"}
    ]
}

python gestalt.py --to ui --input data.json --output screen.ui layout.yml

Auto-detected from .json file extension, or specify with --from json.

EPICS substitutions

Gestalt can read EPICS substitution files (the format used by msi and dbLoadTemplate). This is useful when your PV naming is already defined in a substitutions file:

file "motor.db"
{
    pattern { P, M, PORT }
    { "IOC1:", "m1", "serial1" }
    { "IOC1:", "m2", "serial1" }
    { "IOC1:", "m3", "serial2" }
}

python gestalt.py --to ui --input motors.substitutions --from msi --output screen.ui layout.yml

The parsed data is structured as a dictionary keyed by the database filename. Each key maps to a list of dictionaries (one per substitution row). In the layout, you would reference this as:

Motors: !VRepeat
    repeat-over: "motor.db"
    padding: 5
    children:
        - !Apply:PVReadWrite
            label: "{M}:"
            read-pv: "{P}{M}.RBV"

Auto-detected from .substitutions file extension, or specify with --from msi.

INI / config files

Python-style INI files are also supported:

[settings]
MOTORS = 8
ASPECT = 2.0
PADDING = 15

python gestalt.py --to ui --input config.cfg --output screen.ui layout.yml

Values are accessed as {section[key]} using Python’s format string dictionary access syntax:

Grid: !Grid
    repeat-over: "{settings[MOTORS]}"
    aspect-ratio: "{settings[ASPECT]}"

Auto-detected from .ini and .cfg file extensions, or specify with --from ini.

Format auto-detection

When you use --input without --from, Gestalt infers the format from the file extension:

Extension Format
.yml, .yaml YAML
.json JSON
.substitutions EPICS substitutions
.ini, .cfg INI config

If the extension is not recognized, use --from to specify the format explicitly.

Next steps