class_docstr: PipelineEngine class that computes each term independently.
  
  Parameters
  ----------
  get_loader : callable
      A function that is given a loadable term and returns a PipelineLoader
      to use to retrieve raw data for that term.
  calendar : DatetimeIndex
      Array of dates to consider as trading days when computing a range
      between a fixed start and end.
  asset_finder : catalyst.assets.AssetFinder
      An AssetFinder instance.  We depend on the AssetFinder to determine
      which assets are in the top-level universe at any point in time.
  populate_initial_workspace : callable, optional
      A function which will be used to populate the initial workspace when
      computing a pipeline. See
      :func:`catalyst.pipeline.engine.default_populate_initial_workspace`
      for more info.
  
  See Also
  --------
  :func:`catalyst.pipeline.engine.default_populate_initial_workspace`
code: def __init__(
      self,
      get_loader,
      calendar,
      asset_finder,
      populate_initial_workspace=None,
  ):
      self._get_loader = get_loader
      self._calendar = calendar
      self._finder = asset_finder
  
      self._root_mask_term = AssetExists()
      self._root_mask_dates_term = InputDates()
  
      self._populate_initial_workspace = (
          populate_initial_workspace
          or default_populate_initial_workspace
      )
  
imports: from abc import ABCMeta, abstractmethod
  from uuid import uuid4
  import six
  from six import iteritems, with_metaclass
  from numpy import array
  from pandas import DataFrame, MultiIndex
  from toolz import groupby, juxt
  from toolz.curried.operator import getitem
  from catalyst.lib.adjusted_array import ensure_adjusted_array, ensure_ndarray
  from catalyst.errors import NoFurtherDataError
  from catalyst.utils.numpy_utils import as_column, repeat_first_axis, repeat_last_axis
  from catalyst.utils.pandas_utils import explode
  from .term import AssetExists, InputDates, LoadableTerm
  from catalyst.utils.date_utils import compute_date_range_chunks
  from catalyst.utils.pandas_utils import categorical_df_concat
  from catalyst.utils.sharedoc import copydoc
label_desc: Use image node_id 1 to create a new SimplePipelineEngine object from inherited base classes: PipelineEngine with example: obj = SimplePipelineEngine(get_loader, calendar, asset_finder, populate_initial_workspace)