code: def _format_arg(self, name, trait_spec, value):
      if name == "nthreads" and value == 0:
          value = 1
          try:
              from multiprocessing import cpu_count
  
              value = cpu_count()
          except:
              iflogger.warning(
                  "Number of threads could not be computed"
              )
              pass
          return trait_spec.argstr % value
  
      if name == "in_bvec":
          return trait_spec.argstr % (value, self.inputs.in_bval)
      if name == "out_bvec":
          return trait_spec.argstr % (value, self.inputs.out_bval)
  
      return super()._format_arg(name, trait_spec, value)
  
file_path: nipype/nipype/interfaces/mrtrix3/base.py
imports: from looseversion import LooseVersion
  from ...None import logging
  from ...utils.filemanip import which
  from ..base import CommandLineInputSpec, CommandLine, traits, File, isdefined, PackageInfo
label_desc: Use image node_id 1 for calling the MRTrix3Base obj's underlying member method code with example usage: obj._format_arg(name, trait_spec, value) and returns: super, unknown, unknown, unknown