-

cool-RR · cool-RR · commit d2b547737438 · 2013-10-25T22:01:39.000+03:00
diff --git a/source_py3/python_toolbox/cute_iter_tools.py b/source_py3/python_toolbox/cute_iter_tools.py
@@ -315,9 +315,30 @@ def _fill(iterable, fill_value=None, fill_value_maker=None, length=infinity):
                 yield fill_value_maker()
                 
     
+def get_single_if_any(iterable,
+                      exception_on_multiple=Exception('More than one value '
+                                                      'not allowed.')):
+    '''
+    Get the single item of `iterable`, if any.
     
-    
-    
-    
-    
-    
+    If `iterable` has one item, return it. If it's empty, get `None`. If it has
+    more than one item, raise an exception. (Unless
+    `exception_on_multiple=None`.)
+    '''
+    assert isinstance(exception_on_multiple, Exception) or \
+                                                  exception_on_multiple is None
+    iterator = iter(iterable)
+    try:
+        first_item = next(iterator)
+    except StopIteration:
+        return None
+    else:
+        if exception_on_multiple:
+            try:
+                second_item = next(iterator)
+            except StopIteration:
+                return first_item
+            else:
+                raise exception_on_multiple
+        else: # not exception_on_multiple
+            return first_item
diff --git a/source_py3/test_python_toolbox/test_cute_iter_tools/test_get_single_if_any.py b/source_py3/test_python_toolbox/test_cute_iter_tools/test_get_single_if_any.py
@@ -0,0 +1,25 @@
+# Copyright 2009-2013 Ram Rachum.
+# This program is distributed under the MIT license.
+
+from python_toolbox import cute_testing
+
+from python_toolbox.cute_iter_tools import get_single_if_any
+
+
+def test_get_single_if_any():
+    
+    assert get_single_if_any(()) is get_single_if_any([]) is \
+           get_single_if_any({}) is get_single_if_any(iter({})) is \
+           get_single_if_any('') is None
+    
+    assert get_single_if_any(('g',)) == get_single_if_any(['g']) == \
+           get_single_if_any({'g'}) == get_single_if_any(iter({'g'})) == \
+           get_single_if_any('g') == 'g'
+
+    with cute_testing.RaiseAssertor():
+        get_single_if_any(('g', 'e', 'e'))
+
+    with cute_testing.RaiseAssertor():
+        get_single_if_any('gee')
+        
+    assert get_single_if_any('gee', exception_on_multiple=None) == 'g'
