Merge pull request #325 from neutrinoceros/nep18_savetxt

ENH: (NEP 18) implement numpy.savetxt

pyproject.toml

@@ -108,7 +108,8 @@ addopts = "--ignore=benchmarks --ignore=paper --ignore=unyt/_mpl_array_converter
 filterwarnings = [
     "error",
     "ignore:Matplotlib is currently using agg, which is a non-GUI backend, so cannot show the figure.:UserWarning",
-    "ignore:In accordance with NEP 32:DeprecationWarning"
+    "ignore:In accordance with NEP 32:DeprecationWarning",
+    "ignore:distutils Version classes are deprecated. Use packaging.version instead.:DeprecationWarning",
 ]
 
 [tool.coverage.run]

tox.ini

@@ -45,7 +45,7 @@ deps =
     setuptools_scm
 commands =
     # don't do doctests on old numpy versions
-    pytest --cov=unyt --cov-append --basetemp={envtmpdir} -W once
+    pytest --cov=unyt --cov-append --basetemp={envtmpdir}
     coverage report --omit='.tox/*'
 
 [testenv:py38-dependencies]

unyt/_array_functions.py

@@ -1,3 +1,5 @@
+import warnings
+
 import numpy as np
 from packaging.version import Version
 
@@ -605,3 +607,17 @@ def linalg_eigvalsh(a, *args, **kwargs):
         np.linalg.eigvalsh._implementation(a.view(np.ndarray), *args, **kwargs)
         * a.units
     )
+
+
+@implements(np.savetxt)
+def savetxt(fname, X, *args, **kwargs):
+    warnings.warn(
+        "numpy.savetxt does not preserve units, "
+        "and will only save the raw numerical data from the unyt_array object.\n"
+        "If this is the intended behaviour, call `numpy.savetxt(file, arr.d)` "
+        "to silence this warning.\n"
+        "If you want to preserve units, use `unyt.savetxt` "
+        "(and `unyt.loadtxt`) instead.",
+        stacklevel=4,
+    )
+    return np.savetxt._implementation(fname, X.view(np.ndarray), *args, **kwargs)

unyt/tests/test_array_functions.py

@@ -187,7 +187,6 @@
     np.result_type,
     np.roots,
     np.save,
-    np.savetxt,
     np.savez,
     np.savez_compressed,
     np.searchsorted,
@@ -1193,3 +1192,22 @@ def test_eigvals(func):
     w = func(a)
     assert type(w) is unyt_array
     assert w.units == cm
+
+
+def test_savetxt(tmp_path):
+    a = [1, 2, 3] * cm
+    with pytest.raises(
+        UserWarning,
+        match=re.escape(
+            "numpy.savetxt does not preserve units, "
+            "and will only save the raw numerical data from the unyt_array object.\n"
+            "If this is the intended behaviour, call `numpy.savetxt(file, arr.d)` "
+            "to silence this warning.\n"
+            "If you want to preserve units, use `unyt.savetxt` "
+            "(and `unyt.loadtxt`) instead."
+        ),
+    ):
+        np.savetxt(tmp_path / "savefile.npy", a)
+
+    # check that doing what the warning says doesn't trigger any other warning
+    np.savetxt(tmp_path / "savefile.npy", a.d)