classification
Title: inspect.findsource raises exception with empty __init__.py
Type: behavior Stage:
Components: Library (Lib) Versions: Python 3.6, Python 3.5, Python 2.7
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: Alexander Todorov, r.david.murray, ztane
Priority: normal Keywords:

Created on 2016-07-20 12:05 by Alexander Todorov, last changed 2016-07-21 13:44 by r.david.murray.

Messages (5)
msg270867 - (view) Author: Alexander Todorov (Alexander Todorov) Date: 2016-07-20 12:05
$ python2
Python 2.7.5 (default, Oct 11 2015, 17:47:16) 
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import inspect
>>> from pykickstart import handlers
>>> inspect.getsource(handlers)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/inspect.py", line 701, in getsource
    lines, lnum = getsourcelines(object)
  File "/usr/lib64/python2.7/inspect.py", line 690, in getsourcelines
    lines, lnum = findsource(object)
  File "/usr/lib64/python2.7/inspect.py", line 538, in findsource
    raise IOError('could not get source code')
IOError: could not get source code
>>> 

There is a `pykickstart/handlers/__init__.py` file which is empty and the above import works fine as you can see. However `inspect.findsource` raises an exception. The same problem exists in Python 3.5 as well. The error comes from here:

    532     module = getmodule(object, file)
    533     if module:
    534         lines = linecache.getlines(file, module.__dict__)
    535     else:
    536         lines = linecache.getlines(file)
    537     if not lines:
    538         raise IOError('could not get source code')


At this point `lines` is an empty list and we raise the exception. I'm hitting this problem when using a mutation testing tool that relies on getsource (which calls findsource). 

One possible workaround is to add a comment in the __init__.py file and everything seems to be working then. Another one is to patch the tool I'm using to take into account empty __init__.py files.
msg270871 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2016-07-20 13:54
I agree that this is inconsistent.  It might be quite tricky to fix, though, unless we special case file.endswith('__init__.py'), which feels like a hack.  But maybe it is appropriate.
msg270911 - (view) Author: Antti Haapala (ztane) * Date: 2016-07-21 11:28
Or perhaps getlines should return [''] for empty regular files?
msg270912 - (view) Author: Antti Haapala (ztane) * Date: 2016-07-21 11:30
It must be noted that `getlines` itself is not documented, and thus there is no backwards-compatibility to preserve really. `getline` returns '' for *any* erroneous line, so it wouldn't affect it.
msg270925 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2016-07-21 13:44
I think someone should propose a patch with tests and we'll evaluate it.  We prefer to retain backward compatibility even on undocumented interfaces, if possible, but yes they are more open to change (though only in a feature release, in general).
History
Date User Action Args
2016-07-21 13:44:17r.david.murraysetmessages: + msg270925
2016-07-21 11:30:03ztanesetmessages: + msg270912
2016-07-21 11:28:17ztanesetnosy: + ztane
messages: + msg270911
2016-07-20 13:54:45r.david.murraysetnosy: + r.david.murray

messages: + msg270871
versions: + Python 3.6
2016-07-20 12:05:58Alexander Todorovcreate