How to check for the existence of a get parameter in flask

You can actually use the default value,

opt_param = request.args.get("something")
if opt_param is None:
    print "Argument not provided"

A more Pythonic way to do the same would be using the in operator:

if 'varname' in request.args:
    # parameter 'varname' is specified
    varname = request.args.get('varname')
else:
    # parameter 'varname' is NOT specified