PEP 616: Fix behavior of code snippets (#1336)

pep-0616.rst

@@ -52,7 +52,7 @@ following behavior::
         self_str = str(self)
 
         if isinstance(prefix, tuple):
-            for option in prefix:
+            for option in tuple(prefix):
                 if not isinstance(option, str):
                     raise TypeError()
                 option_str = str(option)
@@ -79,12 +79,14 @@ following behavior::
         self_str = str(self)
 
         if isinstance(suffix, tuple):
-            for option in suffix:
+            for option in tuple(suffix):
                 if not isinstance(option, str):
                     raise TypeError()
                 option_str = str(option)
 
-                if option_str and self_str.endswith(option_str):
+                if not option_str:
+                    return self_str[:]
+                if self_str.endswith(option_str):
                     return self_str[:-len(option_str)]
 
             return self_str[:]
@@ -98,6 +100,7 @@ following behavior::
         else:
             return self_str[:]
 
+
 Note that without the check for the truthyness of suffixes,
 ``s.cutsuffix('')`` would be mishandled and always return the empty
 string due to the unintended evaluation of ``self[:-0]``.
@@ -142,6 +145,7 @@ methods for control flow instead of testing the lengths as above.
 The two methods will also be added to ``collections.UserString``, with
 similar behavior.
 
+
 Motivating examples from the Python standard library
 ====================================================
 
@@ -231,9 +235,6 @@ cookiejar.py
 test_concurrent_futures.py
 --------------------------
 
-In the following example, the meaning of the code changes slightly,
-but in context, it behaves the same.
-
 - Current::
 
     if name.endswith(('Mixin', 'Tests')):
@@ -262,9 +263,10 @@ as taking an iterable of length-1 strings.  The API could therefore be
 generalized to accept any iterable of strings, which would be
 successively removed as prefixes.  While this behavior would be
 consistent, it would not be obvious for users to have to call
-``'foobar'.cutprefix(('foo,))`` for the common use case of a 
+``'foobar'.lstrip(('foo',))`` for the common use case of a
 single prefix.
 
+
 Remove multiple copies of a prefix
 ----------------------------------
 
@@ -273,19 +275,19 @@ expansion of the ``lstrip``/``rstrip`` API -- repeatedly applying the
 function until the argument is unchanged.  This behavior is attainable
 from the proposed behavior via by the following::
 
-    >>> s = 'foobar' * 100 + 'bar'
-    >>> prefixes = ('bar', 'foo')
+    >>> s = 'FooBar' * 100 + 'Baz'
+    >>> prefixes = ('Bar', 'Foo')
     >>> while len(s) != len(s := s.cutprefix(prefixes)): pass
     >>> s
-    'bar'
+    'Baz'
 
 or the more obvious and readable alternative::
 
-    >>> s = 'foo' * 100 + 'bar'
-    >>> prefixes = ('bar', 'foo')
+    >>> s = 'FooBar' * 100 + 'Baz'
+    >>> prefixes = ('Bar', 'Foo')
     >>> while s.startswith(prefixes): s = s.cutprefix(prefixes)
     >>> s
-    'bar'
+    'Baz'
 
 
 Raising an exception when not found