09.01.18 12:46, Nick Coghlan пише:
On 9 January 2018 at 20:07, Antoine Pitrou <solip...@pitrou.net> wrote:
On Mon, 8 Jan 2018 21:22:56 -0800
Nathaniel Smith <n...@pobox.com> wrote:
I'm surprised that multiprocessing.Connection isn't iterable -- it seems
like an obvious oversight.
What is obvious about making a connection iterable? It's the first
time I see someone requesting this.
If you view them as comparable to subprocess pipes, then it can be
surprising that they're not iterable when using a line-oriented
protocol.
If you instead view them as comparable to socket connections, then the
lack of iteration support seems equally reasonable.
Hence my suggestion of providing a docs recipe showing an example of
wrapping a connection in a generator in order to define a suitable way
of getting from a raw bytestream to iterable chunks.
recv() can raise OSError, and it is more likely than raising OSError in
file's readline(). The user code inside the loop also can perform
writing and can raise OSError. This in the case of line-oriented files
there is a single main source of OSError, but in the case of Connections
there are two possible sources, and you need a way to distinguish errors
raised by recv() and by writing. Currently you just use two different
try-except statements.
while True:
try:
data = conn.recv()
except EOFError:
break
except OSError:
# error on reading
try:
# user code
except OSError:
# error on writing
It is very easy extend the case when don't handle OSError to the case
when handle OSError.
If Connections be iterable the code that don't handle errors looks simple:
for data in conn:
# user code
But this simple code is not correct. When add error handling it will
look like:
while True:
try:
data = next(conn)
except StopIteration:
break
except OSError:
# error on reading
try:
# user code
except OSError:
# error on writing
Not too different from the first example and very differen from the
second example. This feature is not useful if properly handle errors, it
makes the simpler only a quick code when you don't handle errors or
handle them improperly.
Yet one concern: the Connections object has the send() method, generator
objects also have send() methods, but with the different semantic. This
may be confusing.
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