code: def call_graphviz_dot(src, fmt):
      
      try:
          svg = dot(src, T=fmt)
      except OSError as e:  # pragma: nocover
          if e.errno == 2:
              cli.error("""
                 cannot find 'dot'
  
                 pydeps calls dot (from graphviz) to create svg diagrams,
                 please make sure that the dot executable is available
                 on your path.
              """)
          raise
      return svg
docs: Call dot command, and provide helpful error message if we
         cannot find it.