Frankly, I’ve often wanted this for other things that share a similar API, JSON comes to mind. Loading from/saving to a file is a pretty common thing— nice to make it easy. And JSON at least has *s versions for strings, so no confusion there. But it’s been this way a LONG time, and with a general trend of Python becoming more of a systems that scripting language, I don’t see it changing. -CHB PS: you don’t need the context manager — at least in cPython — you can put the open call right in the call to load() -- Christopher Barker, PhD Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython

On Feb 8, 2020, at 13:25, Chris Angelico wrote:

On Sun, Feb 9, 2020 at 8:04 AM Random832 wrote:

...

...

On Fri, Feb 7, 2020, at 13:03, Todd wrote: approaches like opening within the dump or load, which the wiki still recommends [1].

So something like:

with open('myfile.p', 'wb') as f: pickle.dump(myobj, f)

Would be:

pickle.dump(myobj, 'myfile.p')

What if you could write pickle.dump(myobj, with open('myfile.p', 'wb'))?

Or other similar examples such as (with open('myfile')).read() - have the compiler automatically transform the code into equivalent to wrapping the statement in a with block.

Exactly how much code would be wrapped in the 'with' block?

I think the answer there is pretty obvious: it can only be the entire statement that the with expression is contained in. That does raise an issue for lambdas and comprehensions. I think for that case, you need to stop thinking of it as a syntactic transformation and instead think of the semantics directly: the with affects the innermost scope if it’s smaller than the innermost statement, even though there’s no way to rewrite it like that. But then nothing else in Python is defined as a syntactic rewrite, so I don’t think that’s a problem.

On 2020-02-08 6:53 p.m., Bruce Leban wrote:

On Sat, Feb 8, 2020 at 1:22 PM Chris Angelico mailto:rosuav@gmail.com> wrote:

On Sun, Feb 9, 2020 at 8:04 AM Random832 mailto:random832@fastmail.com> wrote: > > On Fri, Feb 7, 2020, at 13:03, Todd wrote:

> What if you could write pickle.dump(myobj, with open('myfile.p', 'wb'))? > > Or other similar examples such as (with open('myfile')).read() - have the compiler automatically transform the code into equivalent to wrapping the statement in a with block. >

Exactly how much code would be wrapped in the 'with' block?

This is an intriguing idea, and in the example it's fairly easy to wrap the entire statement in the with block. It gets a bit more complicated with short-circuit logic. This is a contrived example to make it easier to read:

result = (with alpha()) and ((with beta()) if (with gamma()) else (with delta()))

needs to be interpreted something like:

with _alpha := alpha():

    if _alpha:

        with _gamma:= gamma():

if _gamma:

    with _beta := beta():

        result = beta

else:

    with _delta := delta():

        result = delta

    else:

result = _alpha

I don't think there's anything surprising there although precisely defining the semantics will be a little tricky.

I'd expect it to go more like with alpha() as _alpha:     if _alpha:         with gamma() as _gamma:             if _gamma: with beta() as _beta:     result = _beta else: with delta() as _delta:     result = _delta     else:         result = _alpha and even then I might've messed something up here. This seems about as hard to transform as the halting problem tho, at face value.

--- Bruce

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On Sat, Feb 8, 2020, at 18:06, Random832 wrote:

My own expectation, for what it's worth, would be something like [snip]

After thinking about it some more, I realized that my idea can basically be translated to "all with-expressions in the statement get added to an implicit ExitStack, which is then cleaned up after the statement."

It's also tempting to try to define a way to, e.g. only include it in scope for the evaluation of the condition in if statements and while loops.

On further reflection, I don't think this is worth it in the general case - though the idea of a context manager being opened in each iteration of a while loop's condition not being closed until the end of the loop is concerning.