inspect.getsource(), P302 loader and '<..>' filenames

[stefanmueller]

BPO	20205
Nosy	@bitdancer, @ericsnowcurrently, @serhiy-storchaka

^{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 2014-01-09.13:18:49.708>
labels = ['type-bug', 'library']
title = "inspect.getsource(), P302 loader and '<..>' filenames"
updated_at = <Date 2020-03-18.18:34:51.898>
user = 'https://bugs.python.org/stefanmueller'

bugs.python.org fields:

activity = <Date 2020-03-18.18:34:51.898>
actor = 'brett.cannon'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2014-01-09.13:18:49.708>
creator = 'stefan.mueller'
dependencies = []
files = []
hgrepos = []
issue_num = 20205
keywords = []
message_count = 3.0
messages = ['207736', '207766', '207772']
nosy_count = 4.0
nosy_names = ['r.david.murray', 'eric.snow', 'serhiy.storchaka', 'stefan.mueller']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue20205'
versions = ['Python 2.7', 'Python 3.3', 'Python 3.4']

[stefanmueller]

Following situation

• python 2.7.6

• module loaded via a PEP-302 loader.

• the loader has get_source(fullname)

• assigns a dummy string as a file: module.__file__ == "<mymodule>"

Then

inspect.getsource(module)

throws

IOError: could not get source code

I tired to track this down, and it seems to be caused by linecache.updatecache(..) with has

    if not filename or (filename.startswith('<') and filename.endswith('>')):
        return []

at the beginning.

This seems too restrictive me. Without the 'if' it would try to read the file from disk, and if that fails check if there is a loader, without a loader it returns [], so there would not be any behaviour change for non-loader modules if the 'if' was removed, only an additional disk access.

I suggest to remove the 'if'.

Workaround: Don't use '<>' for the dummy file name, but I've read somewhere that those '<>' are a convention for such use-cases.

[serhiy-storchaka]

There would be behavior change if file '<mymodule>' exists.

[bitdancer]

Maybe the logic needs to be reordered: look for a loader first, before looking for a file on disk. It seems to me the current lookup order might itself be a bug.

Note that the code is the same in python3, so the issue exists there as well.