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Question

Does anybody have a beginner-friendly explanation as to why I get a SyntaxError when I call .get() from within an f-string in Python >3.8?

Problem

When I call dict.get() directly within the f-string I get a SyntaxError. If I store the dict.get() call in a variable and reference the variable in the f-string it works without error.

This works

def new_item():
    desc = request.form.get('description', 'No description found')
    return f'Your new item to insert\nDescription:{desc}'

http://127.0.0.1:5000/new_item displays:

Website returning form['description']

This doesn't work

def new_item():
    return f'Your new item to insert\nDescription:{request.form.get('description', 'No description found')}'

SyntaxError: invalid syntax

File ".\server.py", line 39
    return f'Your new item to insert\nDescription:{request.form.get('description', 'No description found')}'
                                                             ^

My Research

StackOverflow is littered with questions (here, here, here, here) and/or problems that were solved simply by calling an adequate Python version. I do have such a Python version installed and am calling also the appropriate command (in fact, the f-string works in an example above). Anyways, here's the powershell:

> python
Python 3.8.1 (tags/v3.8.1:1b293b6, Dec 18 2019, 23:11:46) [MSC v.1916 64 bit (AMD64)] on win32
davidism
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p6l-richard
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    Can't use single quote string within a single quoted string. Try: `return f"Your new item to insert\nDescription:{request.form.get('description', 'No description found')}"` – DarrylG Apr 14 '20 at 10:56
  • Thanks, for the comment. That was the problem (I got it after doing some more research -- sorry for the latency). If you want you can copy my answer and submit it. I'll accept it and remove my own answer. You've earned it! :) – p6l-richard Apr 14 '20 at 10:58
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    There are a few ways you can put quotes inside strings. As in the other comment, use double quotes on the string and single quotes inside it, or you can go the opposite way - single quotes on the string, and double quotes inside.. or you can use backslashes to escape the quote char, or you could use triple double quotes on the string and then anything inside it.. or triple single quotes.. – Todd Apr 14 '20 at 11:26
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    I would prefer your original, two-line function to trying to cram so much code into a single string literal. – chepner Apr 14 '20 at 13:52
  • By the way, f-strings are available for python >= 3.6 – ywbaek Apr 14 '20 at 14:16

1 Answers1

1

After some additional research (see here), the solution to my problem is the following:

I'm calling the dictionary property with a single quoted string. The f-string literal interprets the single-quote as the end of the string and subsequently throws a SyntaxError.

Solution

1) Instead of calling the dictionary property with a single quote, call it with a double-quote, like so:

def new_item():
    return f'Your new item to insert\nDescription:{request.form.get("description", "No description found")}'

As @Todd pointed out in the comment there are more solutions. For the sake of completeness:

2) Invert 1) -- Use a double-quote for the f-string and single one for any strings inside it.

3) Use backslashes \ to escape the quote char

4) Use triple double quotes on the string and then anything inside it

5) Store the dictionary values separately (just like in the working solution in the question). As @chepner points out this has the advantage of respecting max line length limit and improving readability.

--

Thank you all for contributing via comments. I've upvoted.

p6l-richard
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