[New-bugs-announce] [issue25014] Add contextlib.itercm()

[Ezio Melotti]

New submission from Ezio Melotti:

Add an itercm() function that receives an iterable that supports the context manager protocol (e.g. files) and calls enter/exit without having to use the with statement explicitly.

The implementation is pretty straightforward (unless I'm missing something):

def itercm(cm):
    with cm:
        yield from cm

Example usages:

def cat(fnames):
    lines = chain.from_iterable(itercm(open(f)) for f in fnames)
    for line in lines:
        print(line, end='')

This will close the files as soon as the last line is read.

The __exit__ won't be called until the generator is exhausted, so the user should make sure that it is (if he wants __exit__ to be closed).  __exit__ is still called in case of exception.

Attached a clearer example of how it works.

Do you think this would be a good addition to contextlib (or perhaps itertools)?


P.S. I'm also contemplating the idea of having e.g. it = itercm(fname, func=open) to call func lazily once the first next(it) happens, but I haven't thought in detail about the implications of this.  I also haven't considered how this interacts with coroutines.

----------
components: Library (Lib)
files: itercm-example.txt
messages: 249991
nosy: ezio.melotti, ncoghlan, rhettinger
priority: normal
severity: normal
stage: needs patch
status: open
title: Add contextlib.itercm()
type: enhancement
versions: Python 3.6
Added file: http://bugs.python.org/file40380/itercm-example.txt

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<http://bugs.python.org/issue25014>
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