[New-bugs-announce] [issue46304] Unable to iterate over lines in a file without a block of code

[Jason R. Coombs]

New submission from Jason R. Coombs <jaraco at jaraco.com>:

I'd like to be able to do something pretty fundamental: lazily load lines from a file in a single expression.

Best I can tell, that's not possible in the language without triggering warnings.

One can use 'open' but that triggers a ResourceWarning:

```
$ $PYTHONWARNINGS='error' python -c "lines = open('/dev/null'); tuple(lines)"
Exception ignored in: <_io.FileIO name='/dev/null' mode='rb' closefd=True>
ResourceWarning: unclosed file <_io.TextIOWrapper name='/dev/null' mode='r' encoding='UTF-8'>
```

One can use a `with` statement, but that requires a block of code and can't be written easily in a single expression. One can use `pathlib.Path.read_text().splitlines()`, but that loads the whole file into memory.

This issue affected the pip-run project, which required 5 new lines in order to make such an expression possible (https://github.com/jaraco/pip-run/commit/e2f395d8814539e1da467ac09295922d8ccaf14d).

Can the standard library supply a function or method that would provide this behavior?

----------
components: Library (Lib)
messages: 410075
nosy: jaraco
priority: normal
severity: normal
status: open
title: Unable to iterate over lines in a file without a block of code
versions: Python 3.11

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue46304>
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