[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Douglas Greiman]

Douglas Greiman added the comment:

Bazel has been updated to no longer create symlinks to /dev/null

https://github.com/bazelbuild/bazel/issues/1458

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Brett Cannon]

Brett Cannon added the comment:

Those results are expected as passing in a file by path means it's just read by 
open() and then passed to exec() while the others pass through import itself 
which has the os.path.isfile() check.

Since this is a change from Python 2.7 I would be willing to look at a patch 
that loosened things that was fully backwards-compatible, but it would be an 
enhancement and not a bugfix.

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Douglas Greiman]

Douglas Greiman added the comment:

To be thorough, I looked at non __init__.py source files as well, with erratic 
results.  And who knows what would happen on other OS's.  So a blanket "must be 
a regular file" seems reasonable.

$ ls -l b.*
lrwxrwxrwx 1 dgreiman eng 9 Dec  9 16:05 b.py -> /dev/null

$ python2.7 -m b # Success
$ python2.7 -c 'import b'# Success
$ python2.7 b.py # Success

$ python3.5 b.py # Success
$ python3.5 -m b # Failure
/opt/python3.5/bin/python3.5: No module named b
$ python3.5 -c 'import b'# Failure
Traceback (most recent call last):
  File "", line 1, in 
ImportError: No module named 'b'

$ uname -a
Linux 53334eb940e6 3.13.0-101-generic #148-Ubuntu SMP Thu Oct 20 22:08:32 UTC 
2016 x86_64 GNU/Linux

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Brett Cannon]

Brett Cannon added the comment:

There's probably a place to mention it in the language spec for import and/or 
importlib.

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Douglas Greiman]

Douglas Greiman added the comment:

Is there a reasonable place to document that __init__.py (and probably source 
files in general) must be a "regular file" by the Unix definition, and not a 
device file, socket, etc?

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Brett Cannon]

Brett Cannon added the comment:

Since /dev/null is not a file according to os.path.isfile(), I'm going to close 
this as not a bug.

And to answer Antti's question, it's because the semantics come from the 
original C code where EAFP is not pleasant.

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nosy: +brett.cannon
resolution:  -> not a bug
status: open -> closed

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Terry J. Reedy]

Changes by Terry J. Reedy :


--
stage:  -> test needed
versions: +Python 3.6, Python 3.7 -Python 3.4

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Douglas Greiman]

Douglas Greiman added the comment:

See associated bug filed against Bazel:

https://github.com/bazelbuild/bazel/issues/1458

As for why Bazel does that, it's related to the sandboxing implementation but I 
don't know any details beyond that.

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Eric V. Smith]

Changes by Eric V. Smith :


--
nosy: +eric.smith

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Antti Haapala]

Antti Haapala added the comment:

One question is why doesn't it just try to `open`, but wants to stat first, 
when the python principle has always been EAFP.

--
nosy: +ztane

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Senthil Kumaran]

Senthil Kumaran added the comment:

I wanted to ask, Do you know why bazel does that?

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Senthil Kumaran]

Senthil Kumaran added the comment:

Linking __init__.py to /dev/null is very odd. Do you know bazel does that?

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nosy: +orsenthil

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[issue28425] Python3 ignores __init__.py that are links to /dev/null

[Douglas Greiman]

New submission from Douglas Greiman:

This manifests in the following way: A package directory containing an 
__init__.py that is a symlink to /dev/null is treated as a namespace package 
instead of a regular package.

The Bazel build tool creates many __init__.py files in this way, which is how I 
even ran into this.

Symlinks to regular files seem fine.

--
components: Interpreter Core
files: namespace_package_dev_null.sh
messages: 278544
nosy: dgreiman
priority: normal
severity: normal
status: open
title: Python3 ignores __init__.py that are links to /dev/null
type: behavior
versions: Python 3.4, Python 3.5
Added file: http://bugs.python.org/file45069/namespace_package_dev_null.sh

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