On 30 July 2018 at 20:15, Rudy Matela
Hello,
Hi Rudy,
Do you think it would be nice to allow with statements inside genexps or list comprehensions? The functions __enter__ and __exit__ would be automatically called as iterables are traversed. I am thinking of drafting a PEP about this. Examples:
This
g = (f.read() for fn in filenames with open(fn) as f)
would be equivalent to the following use of a generator function:
def __gen(): for fn in filenames: with open(fn) as f: yield f.read() g = __gen()
Yielding from a with block should be discouraged rather than given special syntax. There is essentially a contradiction between the meaning/purpose of yield (suspend indefinitely) and with (definitely call __exit__). If I partially iterate over g as in for line in g: break then at this point g is suspended and f.__exit__ has not been called, so the file is not closed. I may choose to iterate over g later or not, so it has to remain in suspension just in case. In practice if you do this in CPython then f.__exit__ will *probably* be invoked indirectly by g.__del__ if/when the gc collects g. This defeats the main point of using with-open though which is to avoid depending on the gc for closing files. -- Oscar