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From: Neil Cerutti <neilc@norwich.edu>
Newsgroups: comp.lang.python
Subject: Re: semicolon at end of python's statements
Date: 3 Sep 2013 20:00:47 GMT
Organization: Norwich University
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On 2013-09-03, Neil Cerutti <neilc@norwich.edu> wrote:
> 3.2 and above provide contextlib.ExitStack, which I just now
> learned about.
>
> with contextlib.ExitStack() as stack:
>     _in = stack.enter_context(open('some_file'))
>     _out = stack.enter_context(open('another_file', 'w'))
>
> It ain't beautiful, but it unfolds the nesting and gets rid of
> the with statement's line-wrap problems.

It just occurred to me that in most of my use cases ExitStack
saves me from coming up with a name for the file objects at all,
since they are needed only to make csv objects.

Here's a csv file transformer pattern:

import contextlib
import csv

import transform

with contextlib.ExitStack() as stack:
    reader = csv.DictReader(stack.enter_context(open('some_file', newline='')))
    writer = csv.DictWriter(
        stack.enter_context(open('another_file', 'w', newline='')),
        fieldnames=reader.fieldnames)
    writer.writeheader()
    for record in reader:
        writer.writerow(transform.transform(record))

Too bad it's so dense looking.

-- 
Neil Cerutti