Using a filter will allow for a URL variable to be used as a query filter. The string variable will be checked against the state name field in the database table, and uses a like operator to do a fuzzy comparison (that is, it will get all states that start with 'M' if the state_name variable is 'M':

@app.route('/nba/api/v0.1/state/<state_name>', methods=['GET'])
def get_state_name(state_name):
  states = session.query(State).filter(State.name.like(state_name+"%")).all()
  geoms = {state.id:smapping(to_shape(state.geom)) for state in states}
  data = [{"type": "Feature", "properties":{"state":state.name}, 
  "geometry":{"type":"MultiPolygon", 
  "coordinates":[shapely.geometry.geo.mapping(to_shape(state.geom)["coordinates"]]},
  } for state in states]
  return jsonify({"type": "FeatureCollection","features":data})

This function has no URL parameters and will return the specified fields and geometry of the selected states.