On 22-Aug-16 04:04, Martin Panter wrote:
> Martin Panter added the comment:
>
> The ctypes tests all seem to be protected with code that checks for None, and explicitly skip the test in that case. The skip message should be visible when you run the test in verbose mode.
So at least test/test_something.py run cleanly - but why accept code 
that always returns None - for find_library().

Rather than "hard-code" proper strings in a test - shouldn't the test be 
demonstrating the "failure" of find_library() to return a suitable 
response - when it should not be None.

For example, on AIX the IBM provided /usr/lib/libm.a only has static 
members. So, what has always been wrong (and noone noticed, or is it 
noone cared) the "built-in" test in util.py has, and does, always fail:

root@x064:[/data/prj/aixtools/python/python-2.7.12.0/Lib/ctypes]../../python 
util.py
None
None
None
Traceback (most recent call last):
   File "util.py", line 271, in <module>
     test()
   File "util.py", line 266, in test
     print cdll.LoadLibrary("libm.so")
   File 
"/data/prj/aixtools/python/python-2.7.12.0/Lib/ctypes/__init__.py", line 
440, in LoadLibrary
     return self._dlltype(name)
   File 
"/data/prj/aixtools/python/python-2.7.12.0/Lib/ctypes/__init__.py", line 
362, in __init__
     self._handle = _dlopen(self._name, mode)
OSError:        0509-022 Cannot load module .
         0509-026 System error: A file or directory in the path name 
does not exist.

The documentation says:

The exact functionality is system dependent.

On Linux, |find_library()| tries to run external programs 
(|/sbin/ldconfig|, |gcc|, and |objdump|) to find the library file. It 
returns the filename of the library file.
...
On OS X, |find_library()| tries several predefined naming schemes and 
paths to locate the library, and returns a full pathname if successful:
...
On Windows, |find_library()| searches along the system search path, and 
returns the full pathname, but since there is no predefined naming 
scheme a call like |find_library("c")| will fail and return |None|.

Are you saying the documentation should be updated to read:
On AIX, find_library tries to use the Linux code which generally fails 
and will return None.

And the closing bit:
If wrapping a shared library with |ctypes| 
<https://docs.python.org/2/library/ctypes.html#module-ctypes>, it /may/ 
be better to determine the shared library name at development time, and 
hardcode that into the wrapper module instead of using |find_library()| 
to locate the library at runtime (so forget about developing code for 
multiple platforms - find_library() cannot give you that support.
p.s. On AIX, you must use a hard-coded name to ctypes.CDLL() - and also 
add an extra flag - because even though we said "the exact functionality 
is system dependent" we do not permit new systems to add corrections.

I apologize that my frustration is more than peeking through. But I am 
frustrated. find_library(), unless I completely misunderstand the 
documentation, is a helper function to releave the programmer of needing 
to know the specifics of multiple platforms. My frustration is 
heightened by what I read about the issues with "uuid" - which also 
calls find_library() - so again, on AIX it always returns None -- a) 
find_library is broken; b) there is no libuuid.so or libuuid.a on AIX 
(and c) 4 of the 5 programs also called do not exist on AIX, and the one 
that does generates a different string than is compared to).

I understand - AIX has not been a major (user) platform for python. I am 
amazed that noone from IBM (AIX) development has never shown more interest.
Disclaimer: yes, I work for IBM - but am not a developer. Customers do 
ask me about "why is python so old, why does it not work with XXX" - and 
only because I am inclined to "get to the bottom" did I even start on this.

If the root cause is: "IBM showed no interest X years ago and we, 
python, have no interest now in IBM or AIX" then please just say so - 
and I shall do other things with my time.

In closing - I thought python was multi-platform and I had hoped to be 
of some help in improving python integration with the platform AIX. 
Please, one way or the other, help me lessen my frustration.

Thank you for your time and patience with my rant!

> We could avoid skipping these tests in 2.7 by adding a special case for AIX that loads the library via CDLL("libc.a(shr[_64].o)", RTLD_MEMBER). Like an extension of the special cases already at <https://hg.python.org/cpython/file/v2.7.12/Lib/ctypes/test/test_loading.py#l8>, but we have to set the RTLD_ flag as well as the library name.
>
> ----------
>
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> <http://bugs.python.org/issue27435>
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