[yt-users] how to find virial radius from enzo output

Dear All, How to find virial radius from enzo output. From the following page http://yt-project.org/docs/2.6/reference/api/generated/yt.analysis_modules.h...

I came to know that there is a function called virial_radius(). But how to use it? In the provided example

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vr = halos[0].virial_radius()

what is ' halos[0] ' ?

Thank You