On at least some Unix platforms, uid_t and gid_t are mapped to unsigned int. Python parses the values for chown() into signed ints. This causes an exception when a UID is greater than INT_MAX. For a few releases now, 64-bit Fedora has used UINT_MAX-1 as the UID of the nfsnobody user. Python programs chown'ing to the nfsnobody user encounter this problem. The fix is only two lines and is attached. This issue is also documented in Bug 1747858.