launch_yaml

YAML frontend for the launch package.

README

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

e.children

or:

group:
    scoped: False
    children:
        - executable:
            cmd: ls
        - executable:
            cmd: ps

e.children

It returns a list of launch_xml.Entity wrapping each of the xml children. In the example, the list has two Entity objects wrapping each of the executable tags.

Built-in substitutions

See this document.