Include cause exception details in RuntimeError

[GlenWalker]

If there is any kind of error when importing monotonic a generic RuntimeError is raised, with the description 'no suitable implementation for this system'. We very occasionally see this on a system where monotonic otherwise works correctly. I suspect ctypes.util.find_library is occasionally failing (as it executes ldconfig under the hood), but it is difficult to tell because details of the cause are lost, and replaced with the generic error message. Include details of the cause exception in the RuntimeError description so this information is not lost.

[atdt]

Sorry for the delay.

[atdt]

Why repr and not str?

[GlenWalker]

repr typically includes more information in its output than str. For built-in exceptions str will just return the exception message, while repr will also include the exception class name, which would be useful to me when debugging the issue. Since the error I mentioned above happens infrequently I want to gather as much information about the cause exception as possible.

For example:

import ctypes
import ctypes.util
try:
    ctypes.CDLL(ctypes.util.find_library('c')).missing_function
except Exception as e:
  print 'str', str(e)
  print 'repr', repr(e)

outputs

str /lib/x86_64-linux-gnu/libc.so.6: undefined symbol: missing_function
repr AttributeError('/lib/x86_64-linux-gnu/libc.so.6: undefined symbol: missing_function',)

[jeffreydwalter]

I'm neutral on whether or not the exception is a repr or a str, but it definitely needs to log something more than it does currently. While trying to debug #23 I also had to make this same change for the issue to become clear.

[atdt]

Thank you. I'll cut a new release in the next couple of days.