class_docstr: A Pipeline object represents a collection of named expressions to be
  compiled and executed by a PipelineEngine.
  
  A Pipeline has two important attributes: 'columns', a dictionary of named
  :class:`~zipline.pipeline.Term` instances, and 'screen', a
  :class:`~zipline.pipeline.Filter` representing criteria for
  including an asset in the results of a Pipeline.
  
  To compute a pipeline in the context of a TradingAlgorithm, users must call
  ``attach_pipeline`` in their ``initialize`` function to register that the
  pipeline should be computed each trading day. The most recent outputs of an
  attached pipeline can be retrieved by calling ``pipeline_output`` from
  ``handle_data``, ``before_trading_start``, or a scheduled function.
  
  Parameters
  ----------
  columns : dict, optional
      Initial columns.
  screen : zipline.pipeline.Filter, optional
      Initial screen.
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docstr: Render this Pipeline as a DAG.
  
  Parameters
  ----------
  format : {'svg', 'png', 'jpeg'}
      Image format to render with.  Default is 'svg'.
docstr_tok: ["Render","this","Pipeline","as","a","DAG",".","Parameters","--","--","--","--","--","format",":","{","'svg","'",",","'png","'",",","'jpeg","'","}","Image","format","to","render","with",".","Default","is","'svg","'","."]
code: def show_graph(self, format="svg"):
      """
      Render this Pipeline as a DAG.
  
      Parameters
      ----------
      format : {'svg', 'png', 'jpeg'}
          Image format to render with.  Default is 'svg'.
      """
      g = self.to_simple_graph(AssetExists())
      if format == "svg":
          return g.svg
      elif format == "png":
          return g.png
      elif format == "jpeg":
          return g.jpeg
      else:
          # We should never get here because of the expect_element decorator
          # above.
          raise AssertionError("Unknown graph format %r." % format)
  
imports: import six
  from zipline.errors import UnsupportedPipelineOutput
  from zipline.utils.input_validation import expect_element, expect_types, optional
  from .domain import Domain, GENERIC, infer_domain
  from .graph import ExecutionPlan, TermGraph, SCREEN_NAME
  from .filters import Filter
  from .term import AssetExists, ComputableTerm, Term
label_desc: Use image node_id 10 for calling the Pipeline obj's underlying member method code with example usage: obj.show_graph(format) and returns: g, g, g