Message11409

isdir is implemented in Lib/genericpath.py with the following code:

def isdir(s):
    """Return true if the pathname refers to an existing directory."""
    try:
        st = os.stat(s)
    except os.error:
        return False
    return stat.S_ISDIR(st.st_mode)

In turn the core of the stat function is implemented here; Note that we have differentiated stat functions as well for file descriptors (fstat) and symbolic links (lstat), as well as for Windows (WindowsStatFunction):

https://github.com/jythontools/jython/blob/master/src/org/python/modules/posix/PosixModule.java#L1512

Perhaps Z/OS does not support "unix:*" attributes, or only does so partially. We do know that Java does support https://docs.oracle.com/javase/7/docs/api/java/io/File.html#isDirectory(), and in general the Java implementation will always be more reliable than using other predicates, *if available*.

So that is my recommendation: customize genericpath.py usage to use Java where possible, possibly by some specific Jython extensions in PosixModule.java.