flaskflask-script

Blueprint initialization, can I run a function before first request to blueprint


Is it possible to run a function before the first request to a specific blueprint?

@my_blueprint.before_first_request
def init_my_blueprint():
    print 'yes'

Currently this will yield the following error:

AttributeError: 'Blueprint' object has no attribute 'before_first_request'

Solution

  • The Blueprint equivalent is called @Blueprint.before_app_first_request:

    @my_blueprint.before_app_first_request
    def init_my_blueprint():
        print('yes')
    

    The name reflects that it is called before any request, not just a request specific to this blueprint.

    There is no hook for running code for just the first request to be handled by your blueprint. You can simulate that with a @Blueprint.before_request handler that tests if it has been run yet:

    from threading import Lock
    
    my_blueprint._before_request_lock = Lock()
    my_blueprint._got_first_request = False
    
    @my_blueprint.before_request
    def init_my_blueprint():
        if my_blueprint._got_first_request:
            return
        with my_blueprint._before_request_lock:
            if my_blueprint._got_first_request:
                return
    
            # first request, execute what you need.
            print('yes')
    
            # mark first request handled *last*
            my_blueprint._got_first_request = True
    

    This mimics what Flask does here; locking is needed as separate threads could race to the post to be first.