How to call xacro to convert a file?

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I am mostly trying to do something in gazebo, but need to generate a sdf from some xacro files. I am on Ubuntu, and installed the ros-melodic-xacro package, and it exists, but if I try to run /opt/ros/melodic/bin/xacro I get the following error. What am I missing? Thanks,

Traceback (most recent call last):
File "/opt/ros/melodic/bin/xacro", line 32, in <module> import xacro ImportError: No module named xacro