class_docstr: Pseudo-filter describing whether or not an asset existed on a given day.
  This is the default mask for all terms that haven't been passed a mask
  explicitly.
  
  This is morally a Filter, in the sense that it produces a boolean value for
  every asset on every date.  We don't subclass Filter, however, because
  `AssetExists` is computed directly by the PipelineEngine.
  
  This term is guaranteed to be available as an input for any term computed
  by SimplePipelineEngine.run_pipeline().
  
  See Also
  --------
  zipline.assets.AssetFinder.lifetimes
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code: def _compute(self, today, assets, out):
      raise NotImplementedError(
          "AssetExists cannot be computed directly."
          " Check your PipelineEngine configuration."
      )
  
imports: from abc import ABCMeta, abstractproperty, abstractmethod
  from bisect import insort
  from collections import Mapping
  from weakref import WeakValueDictionary
  from numpy import array, dtype, ndarray
  from six import with_metaclass
  from zipline.assets import Asset
  from zipline.errors import DTypeNotSpecified, InvalidOutputName, NonSliceableTerm, NonWindowSafeInput, NotDType, NonPipelineInputs, TermInputsNotSpecified, TermOutputsEmpty, UnsupportedDType, WindowLengthNotSpecified
  from zipline.lib.adjusted_array import can_represent_dtype
  from zipline.lib.labelarray import LabelArray
  from zipline.utils.input_validation import expect_types
  from zipline.utils.memoize import classlazyval, lazyval
  from zipline.utils.numpy_utils import bool_dtype, categorical_dtype, datetime64ns_dtype, default_missing_value_for_dtype, float64_dtype
  from zipline.utils.sharedoc import templated_docstring, PIPELINE_ALIAS_NAME_DOC, PIPELINE_DOWNSAMPLING_FREQUENCY_DOC
  from .domain import Domain, GENERIC, infer_domain
  from .downsample_helpers import expect_downsample_frequency
  from .sentinels import NotSpecified
label_desc: Use image node_id 2 for calling the AssetExists obj's underlying member method code with example usage: obj._compute(today, assets, out) without return types