Why can't client.message.create() receive an f-string as argument for its body parameter?-CodePudding

I'm building a Flask API, and one of its use cases consists on sending a WhatsApp message to a requested phone number. So far, I've been testing this feature through Twilio's sandbox & phone number in a trial account.

This is my use case code:

def send_greetings(order_id):
    try:
        phone = format_phone_number(
            retrieve_target_phone(order_id)
        )  # Retrieves target phone number and formats it (removes whitespace, etc)

        twilio_client.messages.create(
            from_=f"whatsapp:{current_app.config['TWILIO_WHATSAPP_SENDER']}",
            to=f"whatsapp:{phone}",
            body=build_message(order_id),  # Returns an f-string
        )
    except:
        raise

The code above fails to submit the message, but doesn't raise an exception. However, if I change the body argument from the call to build_message to a regular string, the message is sent. If I change the same parameter to a variable containing an f-string, the message won't be submitted.

It's noteworthy that the message I try to submit doesn't really match any defined template. This is the code for the build_message function:

from flask import current_app

def build_message(order_id: str) -> str:
    return f"¡Hola. Has recibido un regalo y junto con el, un saludo especial. Ve a {current_app.config['FRONTEND_DOMAIN']}/destinatario?order_id={order_id} para revisarlo!"

So why is it that when the parameter is a regular string the message is sent, even although it doesn't match any of the 3 predefined templates, but when it's an f-string it's not submitted?

CodePudding user response：

There's nothing magical about f-strings. The bad behavior must be caused by something else.

There is absolutely no difference in the return values of these two functions:

def hello():
    return "Hello John"

def hello_f():
    name = "John"
    return f"Hello {name}"

Anyone calling these functions would see exactly the same return value: a plain old string. The caller would have absolutely no way of knowing that the string was generated using an f-string template.

So there must be some actual difference in the content of the regular string you're using, vs. the output of the build_message() function.