code: def common_start(sa, sb):
      """Return the longest common substring from the beginning of sa and sb."""
  
      def _iter():
          for a, b in zip(sa, sb):
              if a == b:
                  yield a
              else:
                  return
  
      return "".join(_iter())
  
imports: import inspect
  import itertools
  import numpy
  import os
  from glob import glob
  from dipy.workflows.base import get_args_default
label_desc: Use image node_id 1 for calling a global function with example usage: common_start(sa, sb) and returns: str