code: def is_an_altair_chart(chart):
      # Chart type strings look like: "<class 'altair.vegalite.v3.api.FacetChart'>"
      # Chart, FacetChart, LayerChart, and VConcatChart.
      string_type = str(type(chart))
      return "altair" in string_type and "Chart" in string_type
  
imports: import os
  import tempfile
  from absl.testing import absltest
  import altair
  import pandas
  import tensorflow
  from deepvariant import vcf_stats_vis
label_desc: Use image node_id 1 for calling a global function with example usage: is_an_altair_chart(chart) and returns: unknown