Do not allow builtin functions as tasks. (#519)

Author: tobiasraabe

docs/source/changes.md

@@ -9,8 +9,10 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 
 - {pull}`515` enables tests with graphviz in CI. Thanks to {user}`NickCrews`.
 - {pull}`517` raises an error when the configuration file contains a non-existing path
-  (fixes #514). Also adds a warning if the path is configured as a string and not a list
-  of strings.
+  (fixes #514). It also warns if the path is configured as a string and not a list of
+  strings.
+- {pull}`519` raises an error when builtin functions are wrapped with
+  {func}`~pytask.task`. Closes {issue}`512`.
 
 ## 0.4.4 - 2023-12-04
 

src/_pytask/task_utils.py

@@ -4,6 +4,7 @@
 import inspect
 from collections import defaultdict
 from pathlib import Path
+from types import BuiltinFunctionType
 from typing import Any
 from typing import Callable
 
@@ -84,6 +85,9 @@ def task(
     """
 
     def wrapper(func: Callable[..., Any]) -> Callable[..., Any]:
+        # Omits frame when a builtin function is wrapped.
+        _rich_traceback_omit = True
+
         for arg, arg_name in ((name, "name"), (id, "id")):
             if not (isinstance(arg, str) or arg is None):
                 msg = (
@@ -94,6 +98,16 @@ def wrapper(func: Callable[..., Any]) -> Callable[..., Any]:
 
         unwrapped = inspect.unwrap(func)
 
+        # We do not allow builtins as functions because we would need to use
+        # ``inspect.stack`` to infer their caller location and they are unable to carry
+        # the pytask metadata.
+        if isinstance(unwrapped, BuiltinFunctionType):
+            msg = (
+                "Builtin functions cannot be wrapped with '@task'. If necessary, wrap "
+                "the builtin function in a function or lambda expression."
+            )
+            raise NotImplementedError(msg)
+
         raw_path = inspect.getfile(unwrapped)
         if "<string>" in raw_path:
             path = Path(unwrapped.__globals__["__file__"]).absolute().resolve()

tests/test_task.py

@@ -662,3 +662,20 @@ def task_second():
 
     session = build(paths=tmp_path)
     assert session.exit_code == ExitCode.OK
+
+
+def test_raise_error_with_builtin_function_as_task(runner, tmp_path):
+    source = """
+    from pytask import task
+    from pathlib import Path
+    from datetime import datetime
+
+    task(
+        kwargs={"format": "%y/%m/%d"}, produces=Path("time.txt")
+    )(datetime.utcnow().strftime)
+    """
+    tmp_path.joinpath("task_example.py").write_text(textwrap.dedent(source))
+
+    result = runner.invoke(cli, [tmp_path.as_posix()])
+    assert result.exit_code == ExitCode.COLLECTION_FAILED
+    assert "Builtin functions cannot be wrapped" in result.output