Fix passing repeated tasks to the functional interface. (#719)

Author: tobiasraabe

CHANGELOG.md

@@ -15,6 +15,7 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - {pull}`709` add uv pre-commit check.
 - {pull}`713` removes uv as a test dependency. Closes {issue}`712`. Thanks to {user}`erooke`!
 - {pull}`718` fixes {issue}`717` by properly parsing the `pdbcls` configuration option from config files. Thanks to {user}`MImmesberger` for the report!
+- {pull}`719` fixes repeated tasks with the same function name in the programmatic interface to ensure all tasks execute correctly.
 
 ## 0.5.5 - 2025-07-25
 

docs/source/how_to_guides/functional_interface.ipynb

@@ -50,6 +50,7 @@
 from _pytask.shared import to_list
 from _pytask.shared import unwrap_task_function
 from _pytask.task_utils import COLLECTED_TASKS
+from _pytask.task_utils import parse_collected_tasks_with_task_marker
 from _pytask.task_utils import task as task_decorator
 from _pytask.typing import is_task_function
 
@@ -108,6 +109,10 @@ def _collect_from_paths(session: Session) -> None:
 
 def _collect_from_tasks(session: Session) -> None:
     """Collect tasks from user provided tasks via the functional interface."""
+    # First pass: collect and group tasks by path
+    tasks_by_path: dict[Path | None, list[Any]] = {}
+    non_task_objects = []
+
     for raw_task in to_list(session.config.get("tasks", ())):
         if is_task_function(raw_task):
             if not hasattr(raw_task, "pytask_meta"):
@@ -117,18 +122,31 @@ def _collect_from_tasks(session: Session) -> None:
             name = raw_task.pytask_meta.name
 
         if has_mark(raw_task, "task"):
-            # When tasks with @task are passed to the programmatic interface multiple
-            # times, they are deleted from ``COLLECTED_TASKS`` in the first iteration
-            # and are missing in the later. See #625.
+            # When tasks with @task are passed to the programmatic interface
+            # multiple times, they are deleted from ``COLLECTED_TASKS`` in the first
+            # iteration and are missing in the later. See #625.
             with suppress(ValueError):
                 COLLECTED_TASKS[path].remove(raw_task)
 
-        # When a task is not a callable, it can be anything or a PTask. Set arbitrary
-        # values and it will pass without errors and not collected.
+            # Group tasks by path for parametrization
+            if path not in tasks_by_path:
+                tasks_by_path[path] = []
+            tasks_by_path[path].append(raw_task)
         else:
-            name = ""
-            path = None
-
+            # When a task is not a callable, it can be anything or a PTask. Set
+            # arbitrary values and it will pass without errors and not collected.
+            non_task_objects.append((raw_task, None, ""))
+
+    # Second pass: apply parametrization to grouped tasks
+    parametrized_tasks = []
+    for path, tasks in tasks_by_path.items():
+        # Apply the same parametrization logic as file-based collection
+        name_to_function = parse_collected_tasks_with_task_marker(tasks)
+        for name, function in name_to_function.items():
+            parametrized_tasks.append((function, path, name))
+
+    # Third pass: collect all tasks
+    for raw_task, path, name in parametrized_tasks + non_task_objects:
         report = session.hook.pytask_collect_task_protocol(
             session=session,
             reports=session.collection_reports,

src/_pytask/collect.py

@@ -660,6 +660,64 @@ def test_pass_non_task_to_functional_api_that_are_ignored():
     assert len(session.tasks) == 0
 
 
+@pytest.mark.skipif(
+    sys.platform == "win32" and os.environ.get("CI") == "true",
+    reason="Windows does not pick up the right Python interpreter.",
+)
+def test_repeated_tasks_via_functional_interface(tmp_path):
+    """Test that repeated tasks with the same function name work correctly.
+
+    This test ensures that when multiple tasks with the same function name are passed
+    to pytask.build(), they all get unique IDs and execute correctly, similar to how
+    file-based collection handles repeated tasks.
+    """
+    source = """
+    from pathlib import Path
+    from typing import Annotated
+    from pytask import Product, task, build, ExitCode
+    import sys
+
+    # Create repeated tasks with the same function name
+    tasks = []
+    for i in range(3):
+        def create_data(
+            value: int = i * 10,
+            produces: Annotated[Path, Product] = Path(f"output_{i}.txt")
+        ) -> None:
+            '''Generate data based on a value.'''
+            produces.write_text(str(value))
+
+        tasks.append(create_data)
+
+    if __name__ == "__main__":
+        session = build(tasks=tasks)
+
+        # Verify all tasks were collected and executed
+        assert session.exit_code == ExitCode.OK, f"Exit code: {session.exit_code}"
+        assert len(session.tasks) == 3, f"Expected 3 tasks, got {len(session.tasks)}"
+        assert len(session.execution_reports) == 3
+
+        # Verify each task executed and produced the correct output
+        assert Path("output_0.txt").read_text() == "0"
+        assert Path("output_1.txt").read_text() == "10"
+        assert Path("output_2.txt").read_text() == "20"
+
+        # Verify tasks have unique names with repeated task IDs
+        task_names = [task.name for task in session.tasks]
+        assert len(task_names) == len(set(task_names)), "Task names should be unique"
+        assert all("create_data[" in name for name in task_names), \\
+            f"Task names should contain repeated task IDs: {task_names}"
+
+        sys.exit(session.exit_code)
+    """
+    tmp_path.joinpath("task_module.py").write_text(textwrap.dedent(source))
+    result = run_in_subprocess(
+        (sys.executable, tmp_path.joinpath("task_module.py").as_posix()),
+        cwd=tmp_path,
+    )
+    assert result.exit_code == ExitCode.OK
+
+
 def test_multiple_product_annotations(runner, tmp_path):
     source = """
     from pytask import Product

tests/test_execute.py

@@ -0,0 +1,87 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "0",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from pathlib import Path\n",
+    "from typing import Annotated\n",
+    "\n",
+    "import pytask\n",
+    "from pytask import ExitCode\n",
+    "from pytask import Product"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "1",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Create repeated tasks with the same function name\n",
+    "tasks = []\n",
+    "for i in range(3):\n",
+    "\n",
+    "    def create_data(\n",
+    "        value: int = i * 10,\n",
+    "        produces: Annotated[Path, Product] = Path(f\"data_{i}.txt\"),\n",
+    "    ):\n",
+    "        \"\"\"Generate data based on a value.\"\"\"\n",
+    "        produces.write_text(str(value))\n",
+    "\n",
+    "    tasks.append(create_data)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "id": "2",
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# Test that all tasks execute correctly\n",
+    "session = pytask.build(tasks=tasks)\n",
+    "assert session.exit_code == ExitCode.OK\n",
+    "assert len(session.tasks) == 3, f\"Expected 3 tasks, got {len(session.tasks)}\"\n",
+    "assert len(session.execution_reports) == 3, (\n",
+    "    f\"Expected 3 execution reports, got {len(session.execution_reports)}\"\n",
+    ")\n",
+    "\n",
+    "# Verify each file was created with the correct content\n",
+    "assert Path(\"data_0.txt\").read_text() == \"0\"\n",
+    "assert Path(\"data_1.txt\").read_text() == \"10\"\n",
+    "assert Path(\"data_2.txt\").read_text() == \"20\"\n",
+    "\n",
+    "# Clean up\n",
+    "Path(\"data_0.txt\").unlink()\n",
+    "Path(\"data_1.txt\").unlink()\n",
+    "Path(\"data_2.txt\").unlink()"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": ".venv",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.12.12"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}