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control/mirror_gen.py

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+"""
+A "mirroring" ``stdout`` context manager.
+
+While active, the context manager reverses text output to
+``stdout``::
+
+# BEGIN MIRROR_GEN_DEMO_1
+
+    >>> from mirror_gen import looking_glass
+    >>> with looking_glass() as what:  # <1>
+    ...      print('Alice, Kitty and Snowdrop')
+    ...      print(what)
+    ...
+    pordwonS dna yttiK ,ecilA
+    YKCOWREBBAJ
+    >>> what
+    'JABBERWOCKY'
+
+# END MIRROR_GEN_DEMO_1
+
+
+This exposes the context manager operation::
+
+# BEGIN MIRROR_GEN_DEMO_2
+
+    >>> from mirror_gen import looking_glass
+    >>> manager = looking_glass()  # <1>
+    >>> manager  # doctest: +ELLIPSIS
+    <contextlib._GeneratorContextManager object at 0x...>
+    >>> monster = manager.__enter__()  # <2>
+    >>> monster == 'JABBERWOCKY'  # <3>
+    eurT
+    >>> monster
+    'YKCOWREBBAJ'
+    >>> manager  # doctest: +ELLIPSIS
+    >...x0 ta tcejbo reganaMtxetnoCrotareneG_.biltxetnoc<
+    >>> manager.__exit__(None, None, None)  # <4>
+    >>> monster
+    'JABBERWOCKY'
+
+# END MIRROR_GEN_DEMO_2
+
+"""
+
+
+# BEGIN MIRROR_GEN_EX
+
+import contextlib
+
+
+@contextlib.contextmanager  # <1>
+def looking_glass():
+    import sys
+    original_write = sys.stdout.write  # <2>
+
+    def reverse_write(text):  # <3>
+        original_write(text[::-1])
+
+    sys.stdout.write = reverse_write  # <4>
+    yield 'JABBERWOCKY'  # <5>
+    sys.stdout.write = original_write  # <6>
+
+
+# END MIRROR_GEN_EX