join utils in decouple

decouple.py

@@ -5,7 +5,6 @@
 from shlex import shlex
 from io import open
 from collections import OrderedDict
-from util import strtobool
 
 # Useful for very coarse version differentiation.
 PYVERSION = sys.version_info
@@ -26,6 +25,18 @@
 
 DEFAULT_ENCODING = 'UTF-8'
 
+
+def strtobool(value):
+    _value = value.lower()
+    if _value in {"y", "yes", "t", "true", "on", "1"}:
+        result = True
+    elif _value in {"n", "no", "f", "false", "off", "0"}:
+        result = False
+    else:
+        raise ValueError(" ".join(("invalid truth value", value)))
+    return result
+
+
 class UndefinedValueError(Exception):
     pass
 
@@ -261,7 +272,6 @@ def __init__(self, flat=None, cast=text_type, choices=None):
         self._valid_values.extend(self.flat)
         self._valid_values.extend([value for value, _ in self.choices])
 
-
     def __call__(self, value):
         transform = self.cast(value)
         if transform not in self._valid_values:

tests/test_strtobool.py

@@ -0,0 +1,28 @@
+import pytest
+from decouple import strtobool
+
+
+def test_true_values():
+    true_list = ["y", "yes", "t", "true", "on", "1"]
+    for item in true_list:
+        assert strtobool(item) == 1
+
+
+def test_false_values():
+    false_list = ["n", "no", "f", "false", "off", "0"]
+    for item in false_list:
+        assert strtobool(item) == 0
+
+
+@pytest.mark.parametrize(
+    "test_input,expected",
+    [
+        ("Invalid_Value_1", "invalid truth value Invalid_Value_1"),
+        ("1nv4l1d_V4lu3_2", "invalid truth value 1nv4l1d_V4lu3_2"),
+        ("invalid_value_3", "invalid truth value invalid_value_3"),
+    ],
+)
+def test_eval(test_input, expected):
+    with pytest.raises(ValueError) as execinfo:
+        strtobool(test_input)
+    assert str(execinfo.value) == expected