I disagree that the code can't know what will switch with green threads. They switch on I/O and when explicitly requested. An example of using this to get rid of concurrency control: http://www.underengineering.com/2014/05/22/DIY-NoSql/

If you want to make sure that there are no context switching in certain part of your code, you can do it ASSERT-style, something like:

    # enable this only if you use atomic, so a new module that should be imported before gevent
    in_transaction = False
    if __debug__:
        import greenlet
        old_switch=greenlet.greenlet.switch
        class _greenlet(greenlet.greenlet):
            def switch(*args, **kwargs):
                if in_transaction:
                    raise Exception('Switching context during / atomic')
                old_switch(*args, **kwargs)
        setattr(greenlet, 'greenlet', _greenlet)

    @contextmanager
    def atomic():
        """
            Ensure that a function or a block of code is atomic, raise exception if it's not

            Usage:

            @atomic()
            def myTransaction(...):
                ...

            or 

            with atomic():
                ...
        """
        global in_transaction
        in_transaction = True
        yield
        in_transaction = False