launch_yaml

This package provides an abstraction of the YAML tree.

YAML front-end mapping rules

Accessing yaml attributes

When having an YAML file like:

tag:
    value1: '2'
    value2: 2
    value3: 2.0

If the entity e is wrapping tag, the following statement will be true:

e.get_attr('value1') == '2'
e.get_attr('value2', data_type=int) == 2
e.get_attr('value3', data_type=float) == 2.0

By default, get_attr returns an string and it does type checking. The following code will raise a TypeError:

e.get_attr('value1', data_type=int)
e.get_attr('value2', data_type=float)
e.get_attr('value3')

Allowed types are: - scalar types: str, int, float, bool - An uniform list, e.g.: List[int]. - The list of entities type: List[Entity] (see below).

List is the usual object from the typing package. data_type can also be set to None, in which case any of the following scalar types or uniform lists of them are allowed:

int, float, bool, str

In the case a value can be either an instance of a type or a substitution, the can_be_str argument of get_attr must be used, followed by a call to parser.parse_if_substitutions:

value = e.get_attr('value2', data_type=int, can_be_str=True)
normalized_value = parser.parse_if_substitutions(value)

For checking if an attribute exists, use optional argument:

value = e.get_attr('value', optional=True)
if value is not None:
    do_something(value)

With optional=False (default), AttributeError is raised if it is not found.

Accessing attributes that are also an Entity:

In this yaml:

executable:
    cmd: ls
    env:
        - name: a
        - value: '100'
        - name: b
        - value: 'stuff'

The env children could be accessed doing:

env = e.get_attr('env', data_type=List[Entity])
len(env) == 2
env[0].get_attr('name') == 'a'
env[0].get_attr('value') == '100'
env[1].get_attr('name') == 'b'
env[1].get_attr('value') == 'stuff'

In these cases, e.env is a list of entities, that can be accessed in the same abstract way.

Accessing children:

All the children can be directly accessed. e.g.:

group:
    - executable:
        cmd: ls
    - executable:
        cmd: ps

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Changelog for package launch_yaml

3.10.3 (2026-10-23)

• Add boolean launch argument frontend tests (#1043)
• Contributors: Om Vaghasiya

3.10.2 (2026-10-01)

• Make level attribute required on log action and remove log_info.py (#1024)
• Use the SPDX identifier Apache-2.0 in license declarations (#1013)
• Sandbox environment variables in launch_xml/launch_yaml tests (#1001)
• Contributors: Michael Carroll, Peace. A

3.10.1 (2026-09-02)

• Add string strip substitution (#997)
• fix: parse respawn_max_retries YAML strings (#969)
• Contributors: Dylan Gallagher, Lidang Jiang

3.10.0 (2026-05-07)

3.9.7 (2026-04-09)

• Correct typos (#961)
• Support frontends for PathJoinSubstitution (#943)
• Contributors: Auguste Lalande, Christophe Bedard

3.9.6 (2026-01-12)

• Capture the environment variables in TimerAction (#728)
• Contributors: Sebastian Javier D'Alessandro Szymanowski

3.9.5 (2025-11-07)

• Expose StringJoinSubstitution to frontend (#857)
• Contributors: Christian Ruf

3.9.4 (2025-10-17)

• Fix all/any in xml and yaml launch files (#906)
• Contributors: Matthijs van der Burgh

3.9.3 (2025-10-06)

• Allow providing launch args to include using let in frontends (#848)
• Contributors: Christophe Bedard

3.9.2 (2025-07-29)

• Fix Setuptoolsdeprecations (#898)
• Contributors: mosfet80

3.9.1 (2025-06-19)

• Make sure to install py.typed files (#886)
• Add remaining [py.typed]{.title-ref} (#884)
• Fix [log_*]{.title-ref} warnings (#883)
• Other Logging Implementations with [getLevelNamesMapping]{.title-ref} fix (#866)
• Revert "Add Other Logging Implementations (#858)" (#865) This reverts commit b7b31c45b0eb350deedd282b88398d1ca0d5faf4.
• Add Other Logging Implementations (#858)
• Contributors: Christophe Bedard, Michael Carlstrom

3.9.0 (2025-04-24)

3.8.1 (2025-04-18)

3.8.0 (2025-02-27)

• Add ForEach action to repeat entities using iteration-specific values (#802)
• Stop loading extensions during launch_{xml,yaml} tests. (#820)
• Cleanup the launch dependencies. (#819)
• Contributors: Chris Lalancette, Christophe Bedard

3.7.1 (2024-12-20)

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