ENH: Use elementwise comparisons with 0 rather than boolean casting

3 files changed, 15 insertions, 8 deletions

diff --git a/numpy/core/tests/test_deprecations.py b/numpy/core/tests/test_deprecations.py
index 9004bef30..f0eac24ee 100644
--- a/numpy/core/tests/test_deprecations.py
+++ b/numpy/core/tests/test_deprecations.py
@@ -710,15 +710,19 @@ class TestRaggedArray(_DeprecationTestCase):
 
 class TestTrimZeros(_DeprecationTestCase):
     # Numpy 1.20.0, 2020-07-31
-    @pytest.mark.parametrize("arr", [np.random.rand(10, 10).tolist(),
-                                     np.random.rand(10).astype(str)])
-    def test_deprecated(self, arr):
+    @pytest.mark.parametrize(
+        "arr,exc_type",
+        [(np.random.rand(10, 10).tolist(), ValueError),
+         (np.random.rand(10).astype(str), FutureWarning)]
+    )
+    def test_deprecated(self, arr, exc_type):
         with warnings.catch_warnings():
             warnings.simplefilter('error', DeprecationWarning)
             try:
                 np.trim_zeros(arr)
             except DeprecationWarning as ex:
-                assert_(isinstance(ex.__cause__, ValueError))
+                ex_cause = ex.__cause__
+                assert_(isinstance(ex_cause, exc_type))
             else:
                 raise AssertionError("No error raised during function call")
 
diff --git a/numpy/lib/function_base.py b/numpy/lib/function_base.py
index cd8862c94..96e1c6de9 100644
--- a/numpy/lib/function_base.py
+++ b/numpy/lib/function_base.py
@@ -1631,7 +1631,7 @@ def trim_zeros(filt, trim='fb'):
         # Numpy 1.20.0, 2020-07-31
         warning = DeprecationWarning(
             "in the future trim_zeros will require a 1-D array as input "
-            "that is compatible with ndarray.astype(bool)"
+            "that supports elementwise comparisons with zero"
         )
         warning.__cause__ = ex
         warnings.warn(warning, stacklevel=3)
@@ -1643,7 +1643,11 @@ def trim_zeros(filt, trim='fb'):
 
 def _trim_zeros_new(filt, trim='fb'):
     """Newer optimized implementation of ``trim_zeros()``."""
-    arr = np.asanyarray(filt).astype(bool, copy=False)
+    arr_any = np.asanyarray(filt)
+    with warnings.catch_warnings():
+        # not all dtypes support elementwise comparisons with `0` (e.g. str)
+        warnings.simplefilter('error', FutureWarning)
+        arr = arr_any != 0 if arr_any.dtype != bool else arr_any
 
     if arr.ndim != 1:
         raise ValueError('trim_zeros requires an array of exactly one dimension')
diff --git a/numpy/lib/tests/test_function_base.py b/numpy/lib/tests/test_function_base.py
index 89c1a2d9b..744034e01 100644
--- a/numpy/lib/tests/test_function_base.py
+++ b/numpy/lib/tests/test_function_base.py
@@ -1169,10 +1169,9 @@ class TestTrimZeros:
     a = np.array([0, 0, 1, 0, 2, 3, 4, 0])
     b = a.astype(float)
     c = a.astype(complex)
-    d = np.array([None, [], 1, False, 'b', 3.0, range(4), b''], dtype=object)
 
     def values(self):
-        attr_names = ('a', 'b', 'c', 'd')
+        attr_names = ('a', 'b', 'c')
         return (getattr(self, name) for name in attr_names)
 
     def test_basic(self):