Compare set expression for output to target expression

cgp/genome.py

@@ -359,7 +359,11 @@ def change_address_gene_of_output_node(self, new_address: int, output_node_idx:
         self.dna = dna
 
     def set_expression_for_output(
-        self, dna_insert: List[int], hidden_start_node: int = 0, output_node_idx: int = 0
+        self,
+        dna_insert: List[int],
+        target_expression: str,
+        hidden_start_node: int = 0,
+        output_node_idx: int = 0,
     ):
         """Set an expression for one output node
 
@@ -370,6 +374,9 @@ def set_expression_for_output(
         ----------
         dna_insert: List[int]
             dna segment to be inserted at the first hidden nodes.
+        target_expression: str
+             Expression the output node should compile to. Numbers must be written as float.
+             Defaults to None.
         hidden_start_node: int
             Index of the hidden node, where the insert starts.
             Relative to the first hidden node.
@@ -388,6 +395,23 @@ def set_expression_for_output(
         self.change_address_gene_of_output_node(
             new_address=last_inserted_node, output_node_idx=output_node_idx
         )
+        try:
+            import sympy
+
+        except ModuleNotFoundError:
+            raise ModuleNotFoundError(
+                "Can not check output expression. No module named 'sympy' (extra requirement)"
+            )
+
+        if target_expression is not None:
+            if self._n_outputs > 1:
+                output_as_sympy = CartesianGraph(self).to_sympy()[output_node_idx]
+            else:
+                output_as_sympy = CartesianGraph(self).to_sympy()
+
+            target_expression_as_sympy = sympy.parse_expr(target_expression)
+            if not output_as_sympy == target_expression_as_sympy:
+                raise ValueError("expression of output and target expression do not match")
 
     def reorder(self, rng: np.random.RandomState) -> None:
         """Reorder the genome

test/test_genome.py

@@ -835,17 +835,35 @@ def test_set_expression_for_output(genome_params, rng):
     genome = cgp.Genome(**genome_params)
     genome.randomize(rng)
 
-    new_dna = [0, 0, 1]
-    genome.set_expression_for_output(new_dna)
-
     x_0 = sympy.symbols("x_0")
     x_1 = sympy.symbols("x_1")
+
+    new_dna = [0, 0, 1]
+    genome.set_expression_for_output(new_dna, target_expression="x_0 + x_1")
     assert CartesianGraph(genome).to_sympy() == x_0 + x_1
 
     new_dna = [1, 0, 1]
-    genome.set_expression_for_output(new_dna)
+    genome.set_expression_for_output(dna_insert=new_dna, target_expression="x_0 - x_1")
     assert CartesianGraph(genome).to_sympy() == x_0 - x_1
 
     new_dna = [0, 0, 1, 2, 0, 0, 1, 0, 0, 0, 2, 3]  # x_0+x_1; 1.0; 0; x_0+x_1 + 1.0
-    genome.set_expression_for_output(new_dna)
+    genome.set_expression_for_output(dna_insert=new_dna, target_expression="x_0 + x_1 + 1.0")
     assert CartesianGraph(genome).to_sympy() == x_0 + x_1 + 1.0
+
+    with pytest.raises(ValueError):
+        # setting an int in the str causes an error
+        genome.set_expression_for_output(dna_insert=new_dna, target_expression="x_0 + x_1 + 1")
+        genome.set_expression_for_output(dna_insert=new_dna, target_expression="x_0 + x_1 * 1.0")
+
+    genome2_params = {
+        "n_inputs": 2,
+        "n_outputs": 2,
+        "primitives": (cgp.Add, cgp.Sub, cgp.ConstantFloat),
+    }
+    genome2 = cgp.Genome(**genome2_params)
+    genome2.randomize(rng)
+
+    genome2.set_expression_for_output(
+        new_dna, output_node_idx=1, target_expression="x_0 + x_1 + 1.0"
+    )
+    assert CartesianGraph(genome2).to_sympy()[1] == x_0 + x_1 + 1.0