code: def unix_timestamp(
      date_str: Union[str, Expression[str]] = None,
      format: Union[str, Expression[str]] = None,
  ) -> Expression:
      """
      Gets the current unix timestamp in seconds if no arguments are not specified.
      This function is not deterministic which means the value would be recalculated for each record.
  
      If the date time string date_str is specified, it will convert the given date time string
      in the specified format (by default: yyyy-MM-dd HH:mm:ss if not specified) to unix timestamp
      (in seconds), using the specified timezone in table config.
      """
  
      if date_str is None:
          return _leaf_op("unixTimestamp")
      elif format is None:
          return _unary_op("unixTimestamp", date_str)
      else:
          return _binary_op("unixTimestamp", date_str, format)
  
imports: from typing import Union
  from pyflink import add_version_doc
  from pyflink.java_gateway import get_gateway
  from pyflink.table.expression import Expression, _get_java_expression, TimePointUnit, JsonOnNull
  from pyflink.table.types import _to_java_data_type, DataType
  from pyflink.table.udf import UserDefinedFunctionWrapper
  from pyflink.util.java_utils import to_jarray, load_java_class
label_desc: Use image node_id 29 for calling a global function with example usage: unix_timestamp(date_str, format) and returns: _leaf_op, _unary_op, _binary_op