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mirror.py
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90 lines (70 loc) · 2.14 KB
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"""
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
YKCOWREBBAJ
>>> what # <3>
'JABBERWOCKY'
>>> print('Back to normal.') # <4>
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 # doctest: +ELLIPSIS
<mirror.LookingGlass object at 0x...>
>>> monster = manager.__enter__() # <2>
>>> monster == 'JABBERWOCKY' # <3>
eurT
>>> monster
'YKCOWREBBAJ'
>>> manager # doctest: +ELLIPSIS
>... 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[]
import sys
class LookingGlass:
def __enter__(self): # <1>
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>
sys.stdout.write = self.original_write # <7>
if exc_type is ZeroDivisionError: # <8>
print('Please DO NOT divide by zero!')
return True # <9>
# <10>
# end::MIRROR_EX[]