import isna from a single point

Author: samukweku

src/datatable/__init__.py

@@ -21,7 +21,8 @@
 # IN THE SOFTWARE.
 #-------------------------------------------------------------------------------
 from .frame import Frame
-from .expr import (min, max, sd, sum, count, countna, first, abs, exp, isna,
+from .math import isna
+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,

src/datatable/expr/__init__.py

@@ -21,7 +21,7 @@
 # IN THE SOFTWARE.
 #-------------------------------------------------------------------------------
 from .expr import f, g, Expr
-from .math import abs, log, log10, exp, isna
+from .math import abs, log, log10, exp
 from .reduce import (
         sum, count, countna, first, last, median, min, max, sd, cov, corr, nunique)
 
@@ -36,7 +36,6 @@
     "f",
     "first",
     "g",
-    "isna",
     "last",
     "log",
     "log10",

src/datatable/expr/math.py

@@ -15,16 +15,8 @@
 # limitations under the License.
 # -------------------------------------------------------------------------------
 from datatable.lib import core
-import math
-
-__all__ = ("abs", "exp", "log", "log10", "isna")
-
-
-def isna(iterable):
-    if isinstance(iterable, core.FExpr):
-        return core.isna(iterable)
-    return (iterable is None) or (iterable is math.nan)
 
+__all__ = ("abs", "exp", "log", "log10")
 
 # Deprecated, use math namespace instead
 abs = core.abs

src/datatable/math.py

@@ -48,7 +48,6 @@
     isclose,
     isfinite,
     isinf,
-    isna,
     ldexp,
     lgamma,
     log,