accept integer-valued numbers for Integer (#919)

allows config to cast e.g. the float 4e9 to int without error if the value is unchanged

Author: minrk

tests/test_traitlets.py

@@ -7,6 +7,7 @@
 # also under the terms of the Modified BSD License.
 from __future__ import annotations
 
+import decimal
 import pickle
 import re
 import typing as t
@@ -1391,7 +1392,7 @@ class TestLong(TraitTestBase):
     obj = LongTrait()
 
     _default_value = 99
-    _good_values = [10, -10]
+    _good_values = [10, -10, 10.0, decimal.Decimal("10.0")]
     _bad_values = [
         "ten",
         [10],
@@ -1401,6 +1402,7 @@ class TestLong(TraitTestBase):
         1j,
         10.1,
         -10.1,
+        decimal.Decimal("10.1"),
         "10",
         "-10",
         "10L",

traitlets/traitlets.py

@@ -44,6 +44,7 @@
 import contextlib
 import enum
 import inspect
+import numbers
 import os
 import re
 import sys
@@ -2635,6 +2636,15 @@ def __init__(
         )
 
     def validate(self, obj: t.Any, value: t.Any) -> G:
+        if not isinstance(value, int) and isinstance(value, numbers.Number):
+            # allow casting integer-valued numbers to int
+            # allows for more concise assignment like `4e9` which is a float
+            try:
+                int_value = int(value)
+                if int_value == value:
+                    value = int_value
+            except Exception:
+                pass
         if not isinstance(value, int):
             self.error(obj, value)
         return _validate_bounds(self, obj, value)  # type:ignore[no-any-return]