add boolean to string

pydu/string.py

@@ -141,3 +141,26 @@ def sort(s, reverse=False):
     If reverse is True, sorting given string by descending order.
     """
     return ''.join(sorted(s, reverse=reverse))
+
+
+def boolean(obj):
+    """
+    Convert obj to a boolean value.
+    If obj is string, obj will converted by case-insensitive way:
+        * convert `yes`, `y`, `on`, `true`, `t`, `1` to True
+        * convert `no`, `n`, `off`, `false`, `f`, `0` to False
+        * raising TypeError if other values passed
+    If obj is non-string, obj will converted by bool(obj).
+    """
+
+    try:
+        text = obj.strip().lower()
+    except AttributeError:
+        return bool(obj)
+
+    if text in ('yes', 'y', 'on', 'true', 't', '1'):
+        return True
+    elif text in ('no', 'n', 'off', 'false', 'f', '0'):
+        return False
+    else:
+        raise ValueError("Unable to convert {!r} to a boolean value.".format(text))

tests/test_string.py

@@ -1,6 +1,7 @@
 # coding: utf-8
+import pytest
 from pydu.string import (safeencode, safeunicode, strips, lstrips, rstrips,
-                         common_prefix, common_suffix, sort)
+                         common_prefix, common_suffix, sort, boolean)
 
 
 def test_safeencode():
@@ -53,3 +54,26 @@ def test_common_suffix():
 def test_sort():
     assert sort('acb21') == '12abc'
     assert sort('abc21', reverse=True) == 'cba21'
+
+
+class TestBoolean:
+    def test_accepted_text(self):
+        for text in ('yes', 'y', 'on', 'true', 't', '1'):
+            assert boolean(text)
+            assert boolean(text.upper())
+
+        for text in ('no', 'n', 'off', 'false', 'f', '0'):
+            assert not boolean(text)
+            assert not boolean(text.upper())
+
+    @pytest.mark.parametrize('text', ('a', 'b'))
+    def test_unaccepted_text(self, text):
+        with pytest.raises(ValueError):
+            boolean(text)
+
+    def test_nonstring(self):
+        for obj in (10, [1], {1: 1}):
+            assert boolean(obj)
+
+        for obj in (0, [], {}):
+            assert not boolean(obj)