[Flask] Shouldn't is and == operator work same way while doing string comparisons?

[Arup Rakshit]

Hi,

I am facing a problem with `is` and `==` comparisons. The small below program gives different outputs.  When I use `if book['isbn'] is isbn]` I get an empty output, but `if book['isbn'] == isbn]` gives correct output. Why it is like that?

from flask import Flask, jsonify

app = Flask(__name__)

books = [
    {
        "name": 'Learning Python',
        'isbn': '1449355730',
        'price': 200
    },
    {
        "name": 'Practical Object-Oriented Design: An Agile Primer Using Ruby',
        'isbn': 'B07F88LY9M',
        'price': 210
    }
]


# ….

@app.route('/books/<isbn>')
def get_book_by_isbn(isbn):
    return jsonify([{'name': book['name'], 'price': book['price']} for book in books if book['isbn'] == isbn])


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


Curl program:

~$ curl http://127.0.0.1:5000/books/B07F88LY9M
[]
~$ curl http://127.0.0.1:5000/books/B07F88LY9M
[
  {
    "name": "Practical Object-Oriented Design: An Agile Primer Using Ruby", 
    "price": 210
  }
]


Thanks,

Arup Rakshit
ar at zeit.io