fixed `source_to_function`

CHANGELOG.md

@@ -2,3 +2,4 @@
 
 * updated docs for `Loadable.refresh`
 * added `DefaultDict`
+* fixed `source_to_function`

satella/__init__.py

-__version__ = '2.14.20_a3'
+__version__ = '2.14.20'

satella/coding/misc.py

@@ -113,12 +113,12 @@ def source_to_function(src: tp.Union[tp.Callable, str]) -> tp.Callable[[tp.Any],
     :param src: a callable or a Python string expression
     :return: a callable
     """
-    if callable(src):
-        return src
-    else:
+    if isinstance(src, str):
         q = dict(globals())
         exec('_precond = lambda x: ' + src, q)
         return q['_precond']
+    else:
+        return src
 
 
 def update_attr_if_none(obj: object, attr: str, value: tp.Any,

tests/test_coding/test_predicates.py

 import unittest
 
-
+from satella.coding import source_to_function
 from satella.coding.predicates import x, build_structure
 
 
 class TestPredicates(unittest.TestCase):
 
+    def test_source_to_function(self):
+        y = source_to_function(x)
+        self.assertEqual(y(5), 5)
+
     def test_build_structure(self):
         a = {x: x*2}
         b = [x, x*2, x*3]