code: def from_file (self, file, file_location, project):
          
          if __debug__:
              from .targets import ProjectTarget
              assert isinstance(file, basestring)
              assert isinstance(file_location, basestring)
              assert isinstance(project, ProjectTarget)
          # Check if we've created a target corresponding to this file.
          path = os.path.join(os.getcwd(), file_location, file)
          path = os.path.normpath(path)
  
          if path in self.files_:
              return self.files_ [path]
  
          file_type = b2.build.type.type (file)
  
          result = FileTarget (file, file_type, project,
                               None, file_location)
          self.files_ [path] = result
  
          return result
docs: Creates a virtual target with appropriate name and type from 'file'.
              If a target with that name in that project was already created, returns that already
              created target.
              TODO: more correct way would be to compute path to the file, based on name and source location
              for the project, and use that path to determine if the target was already created.
              TODO: passing project with all virtual targets starts to be annoying.