xmacro is a simple tool to define and parse XML macro. it's inspired by ros/xacro which is an XML macro language desiged for urdf. xmacro looks like a simplified version of ros/xacro, it's simpler, but it works well for xml files like urdf and sdf). in addition it's flexible, and also easy to use.

• xmacro is independent of ROS, you could install it by pip .
• XML namespace isn't used in xmacro, there are some reserved tags: xmacro_include, xmacro_define_value, xmacro_define_block, xmacro_block.
• it provides python api so that we could parse xml file in ROS2 launch file.

Installation

# install by pip
pip install xmacro
# install from source code
git clone https://github.com/gezp/xmacro.git
cd xmacro && sudo python3 setup.py install

examples

# some examples in folder test/xmacro
xmacro test_xmacro_block.xml.xmacro > test_xmacro_block.xml

• Value macro
• Block macro
• Math expressions
• Include
• Python API

Value macro are named values that can be inserted anywhere into the XML document except <xmacro_define_block> block.

xmacro definition

<!--definition of properties -->
<xmacro_define_value name="radius" value="4.3" />
<!--use of properties-->
<circle diameter="${2 * radius}" />

generated xml

<circle diameter="8.6" />

Define block macros with the macro tag <xmacro_define_block>, then specify the macro name and a list of parameters. The list of parameters should be whitespace separated.

The usage of block macros is to define <xmacro_block> which will be replaced with corresponding <xmacro_define_block> block.

xmacro definition

<!--definition of macro-->
<xmacro_define_value name="mass" value="0.2" />
<xmacro_define_block name="box_inertia" params="m x y z">
    <mass>${m}</mass>
    <inertia>
         <ixx>${m*(y*y+z*z)/12}</ixx>
         <ixy>0</ixy>
         <ixz>0</ixz>
         <iyy>${m*(x*x+z*z)/12}</iyy>
         <iyz>0</iyz>
        <izz>${m*(x*x+z*z)/12}</izz>
    </inertia>
</xmacro_define_block>
<!--use of macro-->
<inertial>
     <pose>0 0 0.02 0 0 0</pose>
     <xmacro_block name="box_inertia" m="${mass}" x="0.3" y="0.1" z="0.2"/>
</inertial>

generated xml

<inertial>
    <pose>0 0 0.02 0 0 0</pose>
    <mass>0.2</mass>
    <inertia>
        <ixx>0.0008333333333333335</ixx>
        <ixy>0</ixy>
        <ixz>0</ixz>
        <iyy>0.002166666666666667</iyy>
        <iyz>0</iyz>
        <izz>0.002166666666666667</izz>
    </inertia>
</inertial>

• only support simple parameters (string and number), and block parameters isn't supported.
• it's supported to use other xmacro_block in xmacro_define_block which is recursive definition (the max nesting level is 5).

condition block

a example here (you could find more examples in test/xmacro/test_xmacro_condition.xml.xmacro)

<!--use of macro-->
<inertial>
    <pose>0 0 0.02 0 0 0</pose>
    <xmacro_block name="box_inertia" m="${mass}" x="0.3" y="0.1" z="0.2" condition="${mass==0.2}"/>
</inertial>

• the condition can be True, False, 1, 0, we can also use math expression to define condition, but operator < and > isn't supported in math expression.
• if condition is False or 0, the xmacro_block wou't be loaded.
• condition is reserved attribute of <xmacro_block>, so condition can't be used as params of <xmacro_define_block>.

• within dollared-braces ${xxxx}, you can also write simple math expressions.
• refer to examples of Value macro and Block macro
• it's implemented by calling eval() in python, so it's unsafe for some cases.

You can include other xmacro files by using the <xmacro_include> tag.

• it will include the xmcaro definition with tag <xmacro_define_value> and macros with tag <xmacro_define_block>.

<xmacro_include uri="file://simple_car/model.sdf.xmacro"/>

• The uri for file means to open the file directly.
  • it try to open the file with relative path simple_car/model.sdf.xmacro .
  • you can also try to open file with absolute path /simple_car/model.sdf.xmacro with uri file:///simple_car/model.sdf.xmacro.
• <xmacro_include> supports to include recursively.

you can use xmacro in python easily

from xmacro.xmacro import XMLMacro

xmacro=XMLMacro()
#case1 parse from file
xmacro.set_xml_file(inputfile)
xmacro.generate()
xmacro.to_file(outputfile)

#case2 parse from xml string
xmacro.set_xml_string(xml_str)
xmacro.generate()
xmacro.to_file(outputfile)

#case3 generate to string
xmacro.set_xml_file(inputfile)
xmacro.generate()
xmacro.to_string()

#case4 custom macro value
xmacro.set_xml_file(inputfile)
# use custom dictionary to overwrite global macro value defined by <xmacro_define_value>
kv={"rplidar_a2_h":0.8}
xmacro.generate(kv)
xmacro.to_file(outputfile)

maintainer : Zhenpeng Ge, [email protected]

xmacro is provided under MIT License.