-

cool-RR · cool-RR · commit a03fb085ce2b · 2015-06-09T18:01:38.000+03:00
diff --git a/source_py3/python_toolbox/dict_tools.py b/source_py3/python_toolbox/dict_tools.py
@@ -141,4 +141,32 @@ def get_sorted_values(d, key=None):
     '''
     kwargs = {'key': key,} if key is not None else {}
     return get_tuple(d, sorted(d.keys(), **kwargs))
+    
+    
+def reverse(d):
+    '''
+    Reverse a `dict`, creating a new `dict` where keys and values are switched.
+    
+    Example:
+    
+        >>> reverse({'one': 1, 'two': 2, 'three': 3})
+        {1: 'one', 2: 'two', 3: 'three'})
+        
+    This function requires that:
+    
+      1. The values will be distinct, i.e. no value will appear more than once.
+      2. All the values be hashable.
+      
+    '''
+    new_d = {}
+    for key, value in d.items():
+        if value in new_d:
+            raise Exception(
+                "Value %s appeared twice! Once with a key of %s and then "
+                "again with a key of %s. This function is intended only for "
+                "dicts with distinct values." % (value, key, new_d[value])
+            )
+        new_d[value] = key
+    return new_d
+            
     
diff --git a/source_py3/test_python_toolbox/test_dict_tools/test_devour_items.py b/source_py3/test_python_toolbox/test_dict_tools/test_devour_items.py
@@ -1,14 +1,18 @@
 # Copyright 2009-2015 Ram Rachum.
 # This program is distributed under the MIT license.
 
-'''Test package for `dict_tools.devour_items`.'''
+from python_toolbox import cute_testing
 
 from python_toolbox import dict_tools
 
 
+
+
 def test():
-    '''Test the basic workings of `devour_items`.'''
-    my_dict = {1: 2, 3: 4, 5: 6,}
-    assert set(dict_tools.devour_items(my_dict)) == {(1, 2), (3, 4), (5, 6)}
-    assert not my_dict
-    
+    assert dict_tools.reverse({'one': 1, 'two': 2, 'three': 3}) == \
+                                               {1: 'one', 2: 'two', 3: 'three'}
+    assert dict_tools.reverse({}) == {}
+    with cute_testing.RaiseAssertor():
+        dict_tools.reverse({1: 0, 2: 0})
+    with cute_testing.RaiseAssertor():
+        dict_tools.reverse({1: []})
diff --git a/source_py3/test_python_toolbox/test_dict_tools/test_reverse.py b/source_py3/test_python_toolbox/test_dict_tools/test_reverse.py
@@ -0,0 +1,14 @@
+# Copyright 2009-2015 Ram Rachum.
+# This program is distributed under the MIT license.
+
+'''Test package for `dict_tools.devour_items`.'''
+
+from python_toolbox import dict_tools
+
+
+def test():
+    '''Test the basic workings of `devour_items`.'''
+    my_dict = {1: 2, 3: 4, 5: 6,}
+    assert set(dict_tools.devour_items(my_dict)) == {(1, 2), (3, 4), (5, 6)}
+    assert not my_dict
+    
