flask get method which accepts a parameter : Missing 1 required positional argument

Question

I have the following flask code

from flask import Flask, jsonify, request                                                                                                                                                                          
from webargs import fields                                                                                                                                                                                         
from sqlalchemy import create_engine, MetaData, Table, select                                                                                                                                                      
from flask_cors import CORS                                                                                                                                                                                                                                                                                                                                                                                                           
engine = create_engine('...')                                                                                                                                                                                                                                                                                                                                            
////                                                                                                                                                                                                                                                                                                                                                                                                  
app = Flask(__name__)                                                                                                                                                                                                                                                                                                                                                                                                                 
cors = CORS(app, resources={r"/list*": {"origins": "*"}})                                                                                                                                                                                                                                                                                                                                                                             

@app.route('/list-vessels', methods=['GET'])                                                                                                                                                                       
def list_vessels():                                                                                                                                                                                                    
vessel_list = []                                                                                                                                                                                                   
s = select([vesseldetail.c.Vessel])                                                                                                                                                                                
rp = connection.execute(s)                                                                                                                                                                                         
for row in rp:                                                                                                                                                                                                         
    vessel_list.extend(list(row))                                                                                                                                                                                  
return jsonify(vessel_list)                                                                                                                                                                                                                                                                                                                                                                                                       

@app.route('/list-keydates', methods=['GET'])                                                                                                          
def list_keydates(vesselname):                                                                                                                                                                                         
    vesselname = request.args['vesselname']      
    intervention_list = []                                                                                                                                                                                             
    keydate_list = []                                                                                                                                                                                                  
    s = select([keydate.c.Intervention, keydate.c.Date])                                                                                                                                                               
    s = s.where(keydate.c.VESSEL==vesselname)                                                                                                                                                                          
    rp = connection.execute(s)                                                                                                                                                                                         
    for row in rp:                                                                                                                                                                                                         
        intervention_list.append((row[0]))                                                                                                                                                                                 
        keydate_list.append((row[1]))                                                                                                                                                                                  
    return jsonify({"keydates": keydate_list, "intervention": intervention_list})

if __name__ == '__main__':
    app.run(debug=True)

The second endpoint 'list-keydates' returns a TypeError: list_keydates() missing 1 required positional argument: 'vesselname' even when I pass a vesselname in the query string. What am I doing wrong?

Kenny Aires · Accepted Answer · 2020-03-24T14:03:54.280

The argument vesselname is missing when defining the url, try the following:

...
@app.route('/list-keydates/<vesselname>', methods=['GET'])                                                                                                          
def list_keydates(vesselname):
    intervention_list = []                                                                                                                                                                                             
    keydate_list = []                                                                                                                                                                                                  
    s = select([keydate.c.Intervention, keydate.c.Date])                                                                                                                                                               
    s = s.where(keydate.c.VESSEL==vesselname)  
    ...

url should be http://.../list-keydates/name-of-the-vessel

This way you don't have to get the vesselname from request args, its value will be placed in the variable function.

Hope it suits you well

Hi. This works, thanks! But I would still like to know why the other thing doesn't. How would I need to edit the code so I could use request args? — spheroid, Mar 24 '20 at 14:11
No problem! To use request args, you could remove the argument from your function - e.g: `def list_keydates():` - then call the url in the following way: `http://.../list-keydates?vesselname=name-of-the-vessel`. — Kenny Aires, Mar 24 '20 at 14:17

score 2 · Answer 2 · answered Mar 24 '20 at 13:50

you can also do this

when there is a query string in the URL

http://localhost:5000/list-keydates?vesselname=yourdata

@app.route('/list-keydates', methods=['GET'])                                                                                                          
def list_keydates():
    print(request.args['vesselname']                                                                                                                                                                        
    vesselname = request.args['vesselname']

flask get method which accepts a parameter : Missing 1 required positional argument

2 Answers2