code: def _expression_to_sql(expression, node, context):
      
      _expression_transformers = {
          expressions.LocalField: _transform_local_field_to_expression,
          expressions.Variable: _transform_variable_to_expression,
          expressions.Literal: _transform_literal_to_expression,
          expressions.BinaryComposition: _transform_binary_composition_to_expression,
      }
      expression_type = type(expression)
      if expression_type not in _expression_transformers:
          raise NotImplementedError(
              u'Unsupported compiler expression "{}" of type "{}" cannot be converted to SQL '
              u'expression.'.format(expression, type(expression)))
      return _expression_transformers[expression_type](expression, node, context)
docs: Recursively transform a Filter block predicate to its SQLAlchemy expression representation.
  
      Args:
          expression: expression, the compiler expression to transform.
          node: SqlNode, the SqlNode the expression applies to.
          context: CompilationContext, global compilation state and metadata.
  
      Returns:
          Expression, SQLAlchemy Expression equivalent to the passed compiler expression.