update based on feedback

Author: samukweku

src/datatable/__init__.py

@@ -21,8 +21,8 @@
 # IN THE SOFTWARE.
 #-------------------------------------------------------------------------------
 from .frame import Frame
-from .expr import (min, max, sd, sum, count, first, abs, exp,
-                   last, log, log10, f, g, median, cov, corr, countna, nunique)
+from .expr import (min, max, sd, sum, count, countna, first, abs, exp,
+                   last, log, log10, f, g, median, cov, corr, nunique)
 from .lib._datatable import (
     as_type,
     by,
@@ -123,6 +123,7 @@
     "int8",
     "intersect",
     "iread",
+    "isna",
     "join",
     "last",
     "log",

tests/math/test-isna.py

@@ -48,7 +48,7 @@
 @pytest.mark.parametrize("src", all_sources)
 def test_isna(src):
     DT = dt.Frame(src)
-    RES = DT[:, dt.math.isna(f[0])]
+    RES = DT[:, dt.isna(f[0])]
     assert_equals(RES, dt.Frame([(x is None) for x in src]))