15.11.19 12:40, Jonathan Fine пише:
The original poster wanted, inside 'with' context management, to open
several files. Context management is, roughly speaking, deferred
execution wrapped in a try ... except .... statement.
In case of open() there is no deferred execution. The resource is
acquired in open(), not in __enter__().
The lambda construction also provides for deferred execution. Perhaps
something like
>>> with helper(lambda: open('a'), open('b'), open('c')) as a, b c:
>>> pass
would do what the original poster wanted, for a suitable value of
helper. It certainly gives the parentheses the OP wanted, without
introducing new syntax.
It does not work. File 'a' will be leaked if opening file 'b' is failed.
However, map also provides for deferred execution. It returns an
iterable (not a list).
>>> x = map(open, ['a', 'b', 'c'])
>>> x
<map object at 0x7f8cb5653b70>
>>> next(x)
FileNotFoundError: [Errno 2] No such file or directory: 'a'
So the OP could even write:
>>> with helper(map(open, ['a', 'b', 'c'])) as a, b, c:
>>> pass
for a (different) suitable value of helper.
It can work (the helper can be implemented using ExitStack), although it
looks more clumsy to me than just using line continuations.
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