ENH: improve error messages when add_field received a malformed funct…

…ion argument

nose_unit.cfg

@@ -6,5 +6,5 @@ nologcapture=1
 verbosity=2
 where=yt
 with-timer=1
-ignore-files=(test_load_errors.py|test_load_sample.py|test_commons.py|test_ambiguous_fields.py|test_field_access_pytest.py|test_save.py|test_line_annotation_unit.py|test_eps_writer.py|test_registration.py|test_invalid_origin.py|test_outputs_pytest\.py|test_normal_plot_api\.py|test_load_archive\.py|test_stream_particles\.py|test_file_sanitizer\.py)
+ignore-files=(test_load_errors.py|test_load_sample.py|test_commons.py|test_ambiguous_fields.py|test_field_access_pytest.py|test_save.py|test_line_annotation_unit.py|test_eps_writer.py|test_registration.py|test_invalid_origin.py|test_outputs_pytest\.py|test_normal_plot_api\.py|test_load_archive\.py|test_stream_particles\.py|test_file_sanitizer\.py|test_add_field\.py)
 exclude-test=yt.frontends.gdf.tests.test_outputs.TestGDF

tests/tests.yaml

@@ -201,6 +201,7 @@ other_tests:
      - "--ignore-files=test_outputs_pytest\\.py"
      - "--ignore-files=test_normal_plot_api\\.py"
      - "--ignore-file=test_file_sanitizer\\.py"
+     - "--ignore-file=test_add_field\\.py"
      - "--exclude-test=yt.frontends.gdf.tests.test_outputs.TestGDF"
      - "--exclude-test=yt.frontends.adaptahop.tests.test_outputs"
      - "--exclude-test=yt.frontends.stream.tests.test_stream_particles.test_stream_non_cartesian_particles"

yt/data_objects/tests/test_add_field.py

@@ -0,0 +1,103 @@
+from functools import partial
+
+import pytest
+
+from yt.testing import fake_random_ds
+
+
+def test_add_field_lambda():
+    ds = fake_random_ds(16)
+
+    ds.add_field(
+        ("bacon", "spam"),
+        lambda field, data: data["gas", "density"],
+        sampling_type="cell",
+    )
+
+
+def test_add_field_partial():
+    ds = fake_random_ds(16)
+
+    def _spam(field, data, factor):
+        return factor * data["gas", "density"]
+
+    ds.add_field(
+        ("bacon", "spam"),
+        partial(_spam, factor=1),
+        sampling_type="cell",
+    )
+
+
+def test_add_field_arbitrary_callable():
+    ds = fake_random_ds(16)
+
+    class Spam:
+        def __call__(self, field, data):
+            return data["gas", "density"]
+
+    ds.add_field(("bacon", "spam"), Spam(), sampling_type="cell")
+
+
+def test_add_field_uncallable():
+    ds = fake_random_ds(16)
+
+    class Spam:
+        pass
+
+    with pytest.raises(
+        TypeError, match=r"Expected a callable object, got .* with type .*"
+    ):
+        ds.add_field(("bacon", "spam"), Spam(), sampling_type="cell")
+
+
+def test_add_field_wrong_signature():
+    ds = fake_random_ds(16)
+
+    def _spam(data, field):
+        return data["gas", "density"]
+
+    with pytest.raises(
+        TypeError,
+        match=(
+            r"Received field function <function .*> with invalid signature\. "
+            r"Expected exactly 2 positional parameters \('field', 'data'\), got \('data', 'field'\)"
+        ),
+    ):
+        ds.add_field(("bacon", "spam"), _spam, sampling_type="cell")
+
+
+def test_add_field_wrong_signature_lambda():
+    ds = fake_random_ds(16)
+
+    with pytest.raises(
+        TypeError,
+        match=(
+            r"Received field function <function .*> with invalid signature\. "
+            r"Expected exactly 2 positional parameters \('field', 'data'\), got \('data', 'field'\)"
+        ),
+    ):
+        ds.add_field(
+            ("bacon", "spam"),
+            lambda data, field: data["gas", "density"],
+            sampling_type="cell",
+        )
+
+
+def test_add_field_keyword_only():
+    ds = fake_random_ds(16)
+
+    def _spam(field, *, data):
+        return data["gas", "density"]
+
+    with pytest.raises(
+        TypeError,
+        match=(
+            r"Received field function .* with invalid signature\. "
+            r"field and data parameters must accept positional values \(they cannot be keyword-only\)"
+        ),
+    ):
+        ds.add_field(
+            ("bacon", "spam"),
+            _spam,
+            sampling_type="cell",
+        )

yt/fields/field_detector.py

@@ -101,6 +101,8 @@ def _reshape_vals(self, arr):
         return arr.reshape(self.ActiveDimensions, order="C")
 
     def __missing__(self, item):
+        from yt.fields.derived_field import NullFunc
+
         if not isinstance(item, tuple):
             field = ("unknown", item)
         else:
@@ -115,7 +117,7 @@ def __missing__(self, item):
         # Note that the *only* way this works is if we also fix our field
         # dependencies during checking.  Bug #627 talks about this.
         item = self.ds._last_freq
-        if finfo is not None and finfo._function.__name__ != "NullFunc":
+        if finfo is not None and finfo._function is not NullFunc:
             try:
                 for param, param_v in permute_params.items():
                     for v in param_v:

yt/fields/field_info_container.py

@@ -1,4 +1,6 @@
+import inspect
 from collections import defaultdict
+from collections.abc import Callable
 from numbers import Number as numeric_type
 from typing import Optional, Tuple
 
@@ -355,6 +357,30 @@ def create_function(f):
 
             return create_function
 
+        if not isinstance(function, Callable):
+            # this is compatible with lambdas and functools.partial objects
+            raise TypeError(
+                f"Expected a callable object, got {function} with type {type(function)}"
+            )
+
+        # lookup parameters that do not have default values
+        fparams = inspect.signature(function).parameters
+        nodefaults = tuple(p.name for p in fparams.values() if p.default is p.empty)
+        if nodefaults != ("field", "data"):
+            raise TypeError(
+                f"Received field function {function} with invalid signature. "
+                f"Expected exactly 2 positional parameters ('field', 'data'), got {nodefaults!r}"
+            )
+        if any(
+            fparams[name].kind == fparams[name].KEYWORD_ONLY
+            for name in ("field", "data")
+        ):
+            raise TypeError(
+                f"Received field function {function} with invalid signature. "
+                "field and data parameters must accept positional values "
+                "(they cannot be keyword-only)"
+            )
+
         if isinstance(name, tuple):
             self[name] = DerivedField(name, sampling_type, function, **kwargs)
             return

yt/frontends/amrvac/fields.py

@@ -101,7 +101,6 @@ def _setup_velocity_fields(self, idust=None):
             if not ("amrvac", "m%d%s" % (idir, dust_flag)) in self.field_list:
                 break
             velocity_fn = functools.partial(_velocity, idir=idir, prefix=dust_label)
-            functools.update_wrapper(velocity_fn, _velocity)
             self.add_field(
                 ("gas", f"{dust_label}velocity_{alias}"),
                 function=velocity_fn,

yt/visualization/volume_rendering/off_axis_projection.py

@@ -320,8 +320,8 @@ def off_axis_projection(
         weightfield = ("index", "temp_weightfield")
 
         def _make_wf(f, w):
-            def temp_weightfield(a, b):
-                tr = b[f].astype("float64") * b[w]
+            def temp_weightfield(field, data):
+                tr = data[f].astype("float64") * data[w]
                 return tr.d
 
             return temp_weightfield

yt/visualization/volume_rendering/old_camera.py

@@ -2066,9 +2066,9 @@ def __init__(
             self.weightfield = ("index", "temp_weightfield_%u" % (id(self),))
 
             def _make_wf(f, w):
-                def temp_weightfield(a, b):
-                    tr = b[f].astype("float64") * b[w]
-                    return b.apply_units(tr, a.units)
+                def temp_weightfield(field, data):
+                    tr = data[f].astype("float64") * data[w]
+                    return data.apply_units(tr, field.units)
 
                 return temp_weightfield