code: def exec_python(attr, src, executable="python"):
      
      import subprocess
  
      if isinstance(src, basestring):
          src = [src]
  
      p = popen([executable, "-c", "; ".join(src)],
                stdout=subprocess.PIPE, stderr=subprocess.PIPE)
      out, err = p.communicate()
  
      if p.returncode:
          from rez.exceptions import InvalidPackageError
          raise InvalidPackageError(
              "Error determining package attribute '%s':\n%s" % (attr, err))
  
      return out.strip()
docs: Runs a python subproc to calculate a package attribute.
  
      Args:
          attr (str): Name of package attribute being created.
          src (list of str): Python code to execute, will be converted into
              semicolon-delimited single line of code.
  
      Returns:
          str: Output of python process.