breaking: make empty a property

Author: coroa

linopy/expressions.py

@@ -1347,6 +1347,7 @@ def size(self) -> int:
         """
         return self.vars.size
 
+    @property
     def empty(self) -> bool:
         """
         Get whether the linear expression is empty.

linopy/model.py

@@ -9,10 +9,10 @@
 import logging
 import os
 import re
-from collections.abc import Mapping, Sequence
+from collections.abc import Callable, Mapping, Sequence
 from pathlib import Path
 from tempfile import NamedTemporaryFile, gettempdir
-from typing import Any, Callable
+from typing import Any
 
 import numpy as np
 import pandas as pd
@@ -705,7 +705,7 @@ def add_objective(
             The objective function assigned to the model.
         """
         if not overwrite:
-            assert self.objective.expression.empty(), (
+            assert self.objective.expression.empty, (
                 "Objective already defined."
                 " Set `overwrite` to True to force overwriting."
             )

test/test_linear_expression.py

@@ -541,8 +541,8 @@ def test_linear_expression_loc(x: Variable, y: Variable) -> None:
 
 def test_linear_expression_empty(v: Variable) -> None:
     expr = 7 * v
-    assert not expr.empty()
-    assert expr.loc[[]].empty()
+    assert not expr.empty
+    assert expr.loc[[]].empty
 
 
 def test_linear_expression_isnull(v: Variable) -> None: