def _retry_with_session(self, retryable, func, session, bulk):
        """Execute an operation with at most one consecutive retries

        Returns func()'s return value on success. On error retries the same
        command once.

        Re-raises any exception thrown by func().
        """
        retryable = (retryable and self.retry_writes
                     and session and not session._in_transaction)
        last_error = None
        retrying = False

        def is_retrying():
            return bulk.retrying if bulk else retrying
        # Increment the transaction id up front to ensure any retry attempt
        # will use the proper txnNumber, even if server or socket selection
        # fails before the command can be sent.
        if retryable:
            session._start_retryable_write()
            if bulk:
                bulk.started_retryable_write = True

        while True:
            try:
                server = self._select_server(writable_server_selector, session)
                supports_session = (
                    session is not None and
                    server.description.retryable_writes_supported)
                with self._get_socket(server, session) as sock_info:
                    if retryable and not supports_session:
                        if is_retrying():
                            # A retry is not possible because this server does
                            # not support sessions raise the last error.
                            raise last_error
                        retryable = False
                    return func(session, sock_info, retryable)
            except ServerSelectionTimeoutError:
                if is_retrying():
                    # The application may think the write was never attempted
                    # if we raise ServerSelectionTimeoutError on the retry
                    # attempt. Raise the original exception instead.
                    raise last_error
                # A ServerSelectionTimeoutError error indicates that there may
                # be a persistent outage. Attempting to retry in this case will
                # most likely be a waste of time.
                raise
            except ConnectionFailure as exc:
                if not retryable or is_retrying():
                    raise
                if bulk:
                    bulk.retrying = True
                else:
                    retrying = True
                last_error = exc
            except BulkWriteError as exc:
                if not retryable or is_retrying():
                    raise
                # Check the last writeConcernError to determine if this
                # BulkWriteError is retryable.
                wces = exc.details['writeConcernErrors']
                wce = wces[-1] if wces else {}
                if wce.get('code', 0) not in helpers._RETRYABLE_ERROR_CODES:
                    raise
                if bulk:
                    bulk.retrying = True
                else:
                    retrying = True
                last_error = exc
            except OperationFailure as exc:
                # retryWrites on MMAPv1 should raise an actionable error.
                if (exc.code == 20 and
                        str(exc).startswith("Transaction numbers")):
                    errmsg = (
                        "This MongoDB deployment does not support "
                        "retryable writes. Please add retryWrites=false "
                        "to your connection string.")
                    raise OperationFailure(errmsg, exc.code, exc.details)
                if not retryable or is_retrying():
                    raise
                if exc.code not in helpers._RETRYABLE_ERROR_CODES:
                    raise
                if bulk:
                    bulk.retrying = True
                else:
                    retrying = True
                last_error = exc
Execute an operation with at most one consecutive retries

        Returns func()'s return value on success. On error retries the same
        command once.

        Re-raises any exception thrown by func().
        
stackoverflow/venv/lib/python3.6/site-packages/pymongo/mongo_client.py