As this is only used once in `__init__` (as soon as we know it's installed, we don't have to check anymore), I propose inlining this in the form of
```python
executable_name = _GDB_ARGS[0]
if not distutils.spawn.find_executable(executable_name):
  raise OSError('executable could not be found, is gdb installed?')
```
(Also, a gentle reminder towards [CONTRIBUTING.md](https://github.com/google/pyringe/blob/master/CONTRIBUTING.md). As this project is owned by Google, you'll have to sign a CLA before we can accept pull requests.)