code: def is_variable(x):
      if not isinstance(x, Variable):
          raise TypeError("not a Variable", x)
      return x
  
imports: import numpy
  import pytensor.tensor.basic
  from pytensor.graph.basic import Apply, Variable
  from pytensor.graph.fg import FunctionGraph
  from pytensor.graph.op import Op
  from pytensor.graph.rewriting.basic import MergeOptimizer
  from pytensor.graph.type import Type
label_desc: Use image node_id 1 for calling a global function with example usage: is_variable(x) and returns: x