code: def _print_ImaginaryUnit(self, expr):
      return "1j"
  
imports: from .pycode import PythonCodePrinter, MpmathPrinter
  from .numpy import NumPyPrinter
  from sympy.core.sorting import default_sort_key
label_desc: Use image node_id 1 for calling the NumExprPrinter obj's underlying member method code with example usage: obj._print_ImaginaryUnit(expr) and returns: str