Document behaviour of python when launched on symlink to a script

[j13r]

BPO	14547
Nosy	@ncoghlan, @merwok, @bitdancer
Files	main.py: the script is for a Discord bot hosted on heroku

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2012-04-11.14:42:48.600>
labels = ['3.8', 'type-bug', '3.7', 'docs']
title = 'Python symlink to script behaves unexpectedly'
updated_at = <Date 2021-06-08.13:11:25.380>
user = 'https://bugs.python.org/j13r'

bugs.python.org fields:

activity = <Date 2021-06-08.13:11:25.380>
actor = 'free.abdo.sh'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2012-04-11.14:42:48.600>
creator = 'j13r'
dependencies = []
files = ['50098']
hgrepos = []
issue_num = 14547
keywords = []
message_count = 5.0
messages = ['158039', '158057', '158097', '221842', '395328']
nosy_count = 6.0
nosy_names = ['ncoghlan', 'eric.araujo', 'r.david.murray', 'docs@python', 'j13r', 'free.abdo.sh']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue14547'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

Linked PRs

• gh-58752: Doc: Clarify sys.path[0] behavior for symbolic and hard links #142160

[j13r]

If I have a script
foo/bar.py
import baz

and create a symlink to it, called barhere.py
ln -s foo/bar.py barhere.py

when I run it, it behaves unexpectedly, specifically it behaves differently than if I had copied it here. It prefers to import baz from foo/baz, not from the current folder.

Apparently Python (2.7.2-r3) handles symlinks differently than just looking at the content (everything is a file philosophy in UNIX).

[bitdancer]

The content of a symbolic symlink is a symbolic reference to another location in the file system. If you had used a hard link it would certainly work as you expected.

The behavior with respect to symbolic links ought to be documented here:

http://docs.python.org/using/cmdline.html

but doesn't seem to be.

[ncoghlan]

Specifically, we end up calling os.realpath() (or the C level equivalent) when initialising __main__.__file__ and sys.path[0].

Agreed this behaviour should be documented (and tested!) explicitly.

[BreamoreBoy]

I've removed Tests from the components list as I don't think it belongs there.

[freeabdosh]

hello guys
I am facing problem with my sqlite3 database when i make changes it saves the changes for almost 13 hours and then retakes back all the changes that i made, i am using two threads in my code and i am not committing the data but i set the isolation mode to None,
i was using the same queries with mysql database with setting autocommit to on and it was working fine what could be the problem in your opinion?
we searched and ask a lot about this issue but nothing was helpful.