issue2551142 - Import ... unique constraint failure. Full title: Import of retired node with username after active node fails with unique constraint failure. Fix this in two ways: 1) sort export on keyname, retired status so that retired nodes for a given keyname are before the acive node in the export file. This stops generating a broken export. 2) handle importing a broken export by deactivating/fixing up/clearing the active record's unique index entry temporarily. Redo the import of the retired node and resetting the active record to active. The fixup changes the unique index (keyvalue, __retired__) from (keyvalue, 0) to (keyvalue, -1). Then it retries the failed import of a retired record with keyvalue. I use -1 in case something goes wrong, It makes the record stand out in the database allowing hand recovery if needed. Rather than using -1 I could just use the id of the record like a normal retirement does. If the retry of the import fails (raises exception), reset the active record from -1 back to 0 and raise the exception. If it succeeds, reset the active record from -1 back to 0 and continue the import process. Reset __retired__ from -1 to 0 on every import. I don't think the performance loss from resetting on every exception matters as there should be very few exceptions. Also this makes the code more understandable. There is no reason to leave the -1 value in place and do a bulk rest of -1 to 0 after the class csv file is loaded. Also if a fixup is needed it is logged at level info with the rest of the database logging. Also success of the fixup is logged. Fixup failure generates a propagated exception.

try:
    from secrets import choice, randbelow, token_bytes

    def seed(v=None):
        pass

    is_weak = False
except ImportError:
    import os as _os
    import random as _random

    # prefer to use SystemRandom if it is available
    if hasattr(_random, 'SystemRandom'):
        def seed(v=None):
            pass

        _r = _random.SystemRandom()
        is_weak = False
    else:
        # don't completely throw away the existing state, but add some
        # more random state to the existing state
        def seed(v=None):
            import os, time
            _r.seed((_r.getstate(),
                     v,
                     hasattr(os, 'getpid') and os.getpid(),
                     time.time()))

        # create our own instance so we don't mess with the global
        # random number generator
        _r = _random.Random()
        seed()
        is_weak = True

    choice = _r.choice

    def randbelow(i):
        return _r.randint(0, i - 1)

    if hasattr(_os, 'urandom'):
        def token_bytes(l):
            return _os.urandom(l)
    else:
        def token_bytes(l):
            _bchr = chr if str == bytes else lambda x: bytes((x,))
            return b''.join([_bchr(_r.getrandbits(8)) for i in range(l)])