[BUG] fask.Blueprint name may not contain a '.' character

[achimgaedke]

when passing url_base_pathname="/user/jane.doe/" to the Dash constructor, this ValueError is raised:

$ python
Python 3.10.2 | packaged by conda-forge | (main, Jan 14 2022, 08:02:09) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import dash
>>> dash.__version__
'2.1.0'
>>> app = dash.Dash(__name__, url_base_pathname="/user/jane.doe/")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/conda-envs/envs/data-processing/lib/python3.10/site-packages/dash/dash.py", line 423, in __init__
    self.init_app()
  File "/opt/conda-envs/envs/data-processing/lib/python3.10/site-packages/dash/dash.py", line 450, in init_app
    flask.Blueprint(
  File "/opt/conda-envs/envs/data-processing/lib/python3.10/site-packages/flask/blueprints.py", line 197, in __init__
    raise ValueError("'name' may not contain a dot '.' character.")
ValueError: 'name' may not contain a dot '.' character.
>>> 

I have changed dash.py accordingly:

        assets_blueprint_name = "{}{}".format(
            config.routes_pathname_prefix.replace(".", "_").replace("/", "_"), "dash_assets"
        )

and it works. Sadly I couldn't find a document detailing all forbidden characters.

[achimgaedke]

The requirement was introduced by pallets/flask@7c52614, referring to pallets/flask#4041