add and test _post_load_ (back) (#866)

* add back `post_load`

* test `post_load`

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* confusing `_post_load_` tests

* add comment

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/integration/test_post_load.py

@@ -0,0 +1,64 @@
+import zntrack
+
+
+class NodeWithPostLoad(zntrack.Node):
+    params: float = zntrack.params()
+    outs: float = zntrack.outs()
+
+    def _post_load_(self):
+        self.params += 1
+
+    def run(self):
+        self.outs = self.params
+
+
+class DepsOnPostLoadNode(zntrack.Node):
+    deps: float = zntrack.deps()
+    outs: float = zntrack.outs()
+
+    def run(self):
+        self.outs = self.deps
+
+
+def test_post_load(proj_path):
+    project = zntrack.Project()
+    with project:
+        node = NodeWithPostLoad(params=1)
+
+    assert node.params == 1
+    project.repro()
+
+    n = node.from_rev()
+    assert n.params == 2  # modified by _post_load_
+    assert n.outs == 1
+
+
+def test_post_load_deps(proj_path):
+    project = zntrack.Project()
+
+    with project:
+        node = NodeWithPostLoad(params=1)
+        dep_node = DepsOnPostLoadNode(deps=node.outs)
+        dep_node_2 = DepsOnPostLoadNode(deps=node.params)
+
+    project.repro()
+
+    # post load has not been called
+    assert dep_node.outs == 1
+    assert node.outs == 1
+    assert node.params == 1
+    # assert dep_node_2.deps == 2 # has not been resolved from a connection
+    assert dep_node_2.outs == 2
+
+    # post load has been called
+    n = dep_node.from_rev()
+    assert n.outs == 1
+    assert n.deps == 1
+
+    # _post_load_ will also be called if the node is resolved from a connection
+    n2 = dep_node_2.from_rev(name=dep_node_2.name)
+    assert n2.outs == 2
+    assert n2.deps == 2
+
+    assert node.from_rev().outs == 1
+    assert node.from_rev().params == 2

zntrack/node.py

@@ -54,10 +54,8 @@ def __post_init__(self):
             if not znflow.get_graph() is not znflow.empty_graph:
                 self.name = self.__class__.__name__
 
-    @te.deprecated(
-        "The _post_load_ method was removed. Use __post_init__ in combination with `self.state` instead."
-    )
     def _post_load_(self):
+        """Called after `from_rev` is called."""
         raise NotImplementedError
 
     def run(self):
@@ -146,6 +144,9 @@ def from_rev(
                 _ = getattr(instance, field.name)
 
         instance._external_ = True
+        if not running and hasattr(instance, "_post_load_"):
+            with contextlib.suppress(NotImplementedError):
+                instance._post_load_()
 
         return instance