Refactor of flow tools - OpenGraph.compose (#375)

This commit adapts the existing method `:func: OpenGraph.compose` to the new API introduced in #358.

Author: matulni

CHANGELOG.md

@@ -8,17 +8,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 ### Added
-- #347:
+- #374:
   - Introduced new method `graphix.opengraph.OpenGraph.is_equal_structurally` which compares the underlying structure of two open graphs.
   - Added new method `isclose` to `graphix.fundamentals.AbstractMeasurement` which defaults to `==` comparison.
 
 ### Fixed
 
 ### Changed
+- #374: Adapted existing method `graphix.opengraph.OpenGraph.isclose` to the new API introduced in #358.
+- #375: Adapted existing method `graphix.opengraph.OpenGraph.compose` to the new API introduced in #358.
 
 ## [0.3.3] - 2025-10-23
 
-- #347: Adapted existing method `graphix.opengraph.OpenGraph.isclose` to the new API introduced in #358.
 ### Added
 
 - #343: Circuit exporter to OpenQASM3:

graphix/opengraph.py

@@ -360,25 +360,22 @@ def find_pauli_flow(self: OpenGraph[_M_co]) -> PauliFlow[_M_co] | None:
             correction_matrix
         )  # The constructor returns `None` if the correction matrix is not compatible with any partial order on the open graph.
 
-    # TODO: Generalise `compose` to any type of OpenGraph
-    def compose(
-        self: OpenGraph[Measurement], other: OpenGraph[Measurement], mapping: Mapping[int, int]
-    ) -> tuple[OpenGraph[Measurement], dict[int, int]]:
-        r"""Compose two open graphs by merging subsets of nodes from `self` and `other`, and relabeling the nodes of `other` that were not merged.
+    def compose(self, other: OpenGraph[_M_co], mapping: Mapping[int, int]) -> tuple[OpenGraph[_M_co], dict[int, int]]:
+        r"""Compose two open graphs by merging subsets of nodes from ``self`` and ``other``, and relabeling the nodes of ``other`` that were not merged.
 
         Parameters
         ----------
-        other : OpenGraph
-            Open graph to be composed with `self`.
+        other : OpenGraph[_M_co]
+            Open graph to be composed with ``self``.
         mapping: dict[int, int]
-            Partial relabelling of the nodes in `other`, with `keys` and `values` denoting the old and new node labels, respectively.
+            Partial relabelling of the nodes in ``other``, with ``keys`` and ``values`` denoting the old and new node labels, respectively.
 
         Returns
         -------
-        og: OpenGraph
-            composed open graph
+        og: OpenGraph[_M_co]
+            Composed open graph.
         mapping_complete: dict[int, int]
-            Complete relabelling of the nodes in `other`, with `keys` and `values` denoting the old and new node label, respectively.
+            Complete relabelling of the nodes in ``other``, with ``keys`` and ``values`` denoting the old and new node label, respectively.
 
         Notes
         -----
@@ -399,13 +396,14 @@ def compose(
             raise ValueError("Keys of mapping must be correspond to nodes of other.")
         if len(mapping) != len(set(mapping.values())):
             raise ValueError("Values in mapping contain duplicates.")
+
         for v, u in mapping.items():
             if (
                 (vm := other.measurements.get(v)) is not None
                 and (um := self.measurements.get(u)) is not None
                 and not vm.isclose(um)
             ):
-                raise ValueError(f"Attempted to merge nodes {v}:{u} but have different measurements")
+                raise OpenGraphError(f"Attempted to merge nodes with different measurements: {v, vm} -> {u, um}.")
 
         shift = max(*self.graph.nodes, *mapping.values()) + 1