Linux man page for execvp(3)
<http://man7.org/linux/man-pages/man3/execvp.3.html> says:

> The default search path (used when the environment does not contain
> the variable PATH) shows some variation across systems.  It generally
> includes /bin and /usr/bin (in that order) and may also include the
> current working directory.  On some other systems, the current
> working is included after /bin and /usr/bin, as an anti-Trojan-horse
> measure.  The glibc implementation long followed the traditional
> default where the current working directory is included at the start
> of the search path.  However, some code refactoring during the
> development of glibc 2.24 caused the current working directory to be
> dropped altogether from the default search path.  This accidental
> behavior change is considered mildly beneficial, and won't be
> reverted.

So while having cwd is os.defpath has some historical justification,
now that glibc dropped it from its default PATH, it would be prudent for
Python to follow the suit.