Extracting parameters from a Python F-string

Question

I have a python f-string as follows:

def send_string():
    ticket_id=123
    message = f'{ticket_id} Jira created successfully'
    return message

def extract_ticket_from_message(message):
    #pseudo code
    # Is it possible to extract the ticket id without parsing the 
    # whole string and using regex

Is there a convenient way of extracting the ticket_id value from the f-string without having to parse the whole string using regex in Python 3.6?

Well, the variable ticket_id should hold it. I'm guessing that's not what you're looking for... can you expand a bit? Maybe with a little more example code? — glibdud
– glibdud, Commented Nov 15, 2018 at 18:23
is "ticket_id" literally the expected output in your example, or are you expecting a ticket id like "1234"? Does the solution need to be generalized? Do we have any garauntees about what ticket_id is going to be: i.e.- do we know it won't contain spaces and you can simply use message.split(maxsplit=1)[0]? — Reid Ballard
– Reid Ballard, Commented Nov 15, 2018 at 18:23
Why not simply yourDesiredResult = str(ticket_id)? Is this an XY problem? — Jongware
– Jongware, Commented Nov 15, 2018 at 18:26
@Austin: in the formatted f-string it will be a string. It looks like OP is thinking about alternatives to getting its value as a string. We will have to await clarification, though. — Jongware
– Jongware, Commented Nov 15, 2018 at 18:30

Jongware · Accepted Answer · 2018-11-16 10:28:01Z

1

If

 ticket_id = 1234
 message = f'{ticket_id} Jira created successfully'

then – without using a regex –

def extract_ticket_from_message(message):
    return message.split()[0]

In other words, the first word. If ticket_id can be any string as well (so possibly containing spaces), you can still use this but cut off the final 3 words instead. (After all, you know what will follow.) If ticket_id is a more complex object that results in a string representation, there is no practical way to resolve it back to the original class/object/anything else than a Python primitive.

Noteworthy: you cannot get the original type without ambiguity. If the original was a string but its value was "1234", then you cannot know for sure if a string or number was passed.

edited Nov 16, 2018 at 10:28

answered Nov 15, 2018 at 18:34

Jongware

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