sync with O'Reilly Atlas

18-with-match/mirror.py

@@ -0,0 +1,92 @@
+"""
+A "mirroring" ``stdout`` context.
+
+While active, the context manager reverses text output to
+``stdout``::
+
+# tag::MIRROR_DEMO_1[]
+
+    >>> from mirror import LookingGlass
+    >>> with LookingGlass() as what:  # <1>
+    ...      print('Alice, Kitty and Snowdrop')  # <2>
+    ...      print(what)
+    ...
+    pordwonS dna yttiK ,ecilA  # <3>
+    YKCOWREBBAJ
+    >>> what  # <4>
+    'JABBERWOCKY'
+    >>> print('Back to normal.')  # <5>
+    Back to normal.
+
+# end::MIRROR_DEMO_1[]
+
+
+This exposes the context manager operation::
+
+# tag::MIRROR_DEMO_2[]
+
+    >>> from mirror import LookingGlass
+    >>> manager = LookingGlass()  # <1>
+    >>> manager
+    <mirror.LookingGlass object at 0x2a578ac>
+    >>> monster = manager.__enter__()  # <2>
+    >>> monster == 'JABBERWOCKY'  # <3>
+    eurT
+    >>> monster
+    'YKCOWREBBAJ'
+    >>> manager
+    >ca875a2x0 ta tcejbo ssalGgnikooL.rorrim<
+    >>> manager.__exit__(None, None, None)  # <4>
+    >>> monster
+    'JABBERWOCKY'
+
+# end::MIRROR_DEMO_2[]
+
+The context manager can handle and "swallow" exceptions.
+
+# tag::MIRROR_DEMO_3[]
+
+    >>> from mirror import LookingGlass
+    >>> with LookingGlass():
+    ...      print('Humpty Dumpty')
+    ...      x = 1/0  # <1>
+    ...      print('END')  # <2>
+    ...
+    ytpmuD ytpmuH
+    Please DO NOT divide by zero!
+    >>> with LookingGlass():
+    ...      print('Humpty Dumpty')
+    ...      x = no_such_name  # <1>
+    ...      print('END')  # <2>
+    ...
+    Traceback (most recent call last):
+      ...
+    NameError: name 'no_such_name' is not defined
+
+# end::MIRROR_DEMO_3[]
+
+"""
+
+
+# tag::MIRROR_EX[]
+class LookingGlass:
+
+    def __enter__(self):  # <1>
+        import sys
+        self.original_write = sys.stdout.write  # <2>
+        sys.stdout.write = self.reverse_write  # <3>
+        return 'JABBERWOCKY'  # <4>
+
+    def reverse_write(self, text):  # <5>
+        self.original_write(text[::-1])
+
+    def __exit__(self, exc_type, exc_value, traceback):  # <6>
+        import sys  # <7>
+        sys.stdout.write = self.original_write  # <8>
+        if exc_type is ZeroDivisionError:  # <9>
+            print('Please DO NOT divide by zero!')
+            return True  # <10>
+        # <11>
+
+
+# end::MIRROR_EX[]