flask database global variable - flask

Question

in my flask app I am using mongoDB and on the home page I have a form that is returning all the known collections in that particular database. I am asking the user to pick a collection they want to use as I will use that collection set to return all the documents in other routes or views.
Im struggling how to make this global "selected_collection" a global variable that all the routes and views can use.
for example on the index page I am able select a collection then on the submit it would redirect me to view db_selected there I was trying to make the selected_collection a global variable but if i got to the about view it get an error related to
I imagine I should use flask.g but im not sure how to get it to work. I have read some of the documents but they are a little vague to me.
AttributeError: '_AppCtxGlobals' object has no attribute 'selected_collection'
how can i make this work?
app.py file:
# INDEX
#app.route('/', methods=['GET', 'POST'])
def index():
coll_name = get_db_collection()
return render_template('index.html', coll_name=coll_name)
# LOGIN
#app.route('/db_selected', methods=['GET', 'POST'])
def db_selected():
if request.method == 'POST':
selected_collection = request.form['Item_4']
selected_collection = g.selected_collection
return render_template('db_selected.html',
selected_collection=selected_collection)
#app.route('/about')
def about():
app.logger.info('selected_collection is {}'.format(g.selected_collection))
return render_template('about.html')
index.html file:
{%extends 'layout.html'%}
{%block body%}
<div class="jumbotron text-center">
<h1>Welcome to the index.html file !</h1>
</div>
<div class="container">
{% include 'db_query_bar.html' %}
</div>
{%endblock%}
db_query_bar.html
<form class="form-horizontal" action="{{ url_for('db_selected') }}" name="Item_1" method="POST">
<fieldset>
<legend>Select DB</legend>
<div class="form-group">
<label for="select" class="col-lg-2 control-label">Database Collection:</label>
<select id="DB" class="form-control" name="Item_4" style="width: 70%" >
<!-- <option value="">All</option> -->
{% for item in coll_name %}
<option value="{{item}}">{{item}}</option>
{% endfor %}
</select>
<br>
</div>
<div class="form-group">
<div class="col-lg-10 col-lg-offset-2">
<button type="submit" class="btn btn-success">Submit</button>
</div>
</div>
</fieldset>
</form>

Answer 1

Just to answer this for the global variable I ended up placing
app.selected_collection = "Some Value"
in the top of my flask code this will create a global variable I can use in all the views.
app = Flask(__name__)
# CONFIG MONGO CONNECTION DETAILS
app.config['MONGO_HOST'] = 'DB-Host'
app.config['MONGO_DBNAME'] = 'DB-Collection'
app.selected_collection = "Some Value"
# INIT MONGODB
mongo = PyMongo(app)