Kristján Valur Jónsson <swesk...@gmail.com> added the comment:
Having given this some thougt, years laters, I believe it _is_ possible to
write nested() (and nested_delayed()) in a correct way in python, without the
ContextManagerExit function.
Behold!
import contextlib
@contextlib.contextmanager
def nested_delayed(*callables):
"""
Instantiate and invoke context managers in a nested way. each argument
is a callable which
returns an instantiated context manager
"""
if len(callables) > 1:
with nested_delayed(*callables[:-1]) as a, callables[-1]() as b:
yield a + (b,)
elif len(callables) == 1:
with callables[0]() as a:
yield (a,)
else:
yield ()
def nested(*managers):
"""
Invoke preinstantiated context managers in a nested way
"""
def helper(m):
"""
A helper that returns the preinstantiated context manager when
invoked
"""
def callable():
return m
return callable
return nested_delayed(*(helper(m) for m in managers))
@contextlib.contextmanager
def ca():
print("a")
yield 1
class cb:
def __init__(self):
print ("instantiating b")
def __enter__(self):
print ("b")
return 2
def __exit__(*args):
pass
@contextlib.contextmanager
def cc():
print("c")
yield 3
combo = nested(ca(), cb(), cc())
combo2 = nested_delayed(ca, cb, cc)
with combo as a:
print("nested", a)
with combo2 as a:
print("nested_delayed", a)
with ca() as a, cb() as b, cc() as c:
print ("syntax", (a, b, c))
----------
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue18677>
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