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

Question

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'

Answer 1

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.