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