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Substitutions for string manipulations and xacro #741

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nlamprian opened this issue Nov 4, 2023 · 4 comments · May be fixed by #838
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Substitutions for string manipulations and xacro #741

nlamprian opened this issue Nov 4, 2023 · 4 comments · May be fixed by #838
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@christophebedard

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@nlamprian
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Feature request

Feature description

Coming back with another request for a substitution... I tried using a path join substitution with a filename that depends on a launch configuration. The path join substitution does not allow one to concatenate parts of a filename. It ended up using a python expression.

xacro_filename = PythonExpression(["'", LaunchConfiguration("model"), "' + '.xacro'"])
xacro_filepath = PathJoinSubstitution(["robot_description", "urdf", xacro_filename])

Implementation considerations

I would have hoped that text substitution could take multiple texts so that I could do

TextSubstitution(LaunchConfiguration("model"), ".xacro")

But this is not compatible, given how text substitution was put together.

So, how about having a substitution that concatenates strings and then also having the separator parameterized?

In the simple case, one would do

StringSubstitution([LaunchConfiguration("model"), ".xacro"])  # -> "model_value.xacro"

And then, this could be used in other practical ways, for example, to create a xacro substitution

class XacroSubstitution(Command):
    def __init__(
        self, 
        filepath: SomeSubstitutionsType, 
        arg_str: SomeSubstitutionsType = "",  # xacro arguments that are passed as a launch argument
        arg_dict: Dict = None,  # xacro arguments that are defined in the launch file
    ):
        command = [FindExecutable(name="xacro"), " ", filepath, " "]
        arg_str, arg_dict = normalize_to_list_of_substitutions(arg_str), arg_dict or {}
        arg_list = [StringSubstitution([key, value], sep=":=") for key, value in arg_dict.items()]
        command.extend(StringSubstitution(arg_list + arg_str, sep=" "))
        super().__init__(command)
@matosinho
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I did the same with Python expression for ".sdf". That was the exact thing I tried, to use a list with TextSubstitution, but then I discovered that it was not possible. Nice suggestion!

@bektaskemal bektaskemal mentioned this issue Mar 19, 2024
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@dvdmc dvdmc mentioned this issue Mar 14, 2025
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@christophebedard
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christophebedard commented Mar 16, 2025 •
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I wonder if we could make SomeSubstitutionsType accept lists of lists of text/substitutions, similar to what @dvdmc suggested in #835 (comment). Something like:

SomeSubstitutionsType = Union[
    Text,
    Substitution,
    Iterable[Union[Text, Substitution, Iterable[Text, Substitution]]],
]

I don't know if this is doable in practice or if it has any unforeseen implications. If anyone could give it a try and find out, it would be appreciated! Or maybe adding a substitution like #768 does helps prevent us from opening a can of worms?

@christophebedard
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christophebedard commented Mar 16, 2025 •
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Wait, PathJoinSubstitution currently takes in an Iterable[Union[Text, Substitution]], not a SomeSubstitutionsType:

launch/launch/launch/substitutions/path_join_substitution.py

Line 29 in 151b024

def __init__(self, substitutions: Iterable[Union[Text, Substitution]]) -> None:

If it took in an Iterable[SomeSubstitutionsType], then the example in #835 (comment) might be possible. That makes more sense for PathJoinSubstitution, since it joins strings into a path.

@christophebedard christophebedard linked a pull request Mar 16, 2025 that will close this issue
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@christophebedard
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@dvdmc @nlamprian @matosinho: please see #838. It improves PathJoinSubstitution to allow something like:

PathJoinSubstitution(['robot_description', 'urdf', [LaunchConfiguration('model'), '.xacro']])

@christophebedard christophebedard marked this as a duplicate of #844 Mar 23, 2025
@christophebedard christophebedard self-assigned this Mar 27, 2025
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Allow concatenating each path component of PathJoinSubstitution ros2/launch
3 participants
@nlamprian @christophebedard @matosinho