5 ms·

Python f-strings are the best syntax sugar i never knew about

15 points by pyedpiper 9y ago

I've written `"text {foo}".format(foo=foo)` so many times I've almost convinced myself that it's not that verbose. Then i discovered fstrings introduced ins 3.6: ``` >>> f"text {fpp}" 'text foo' ``` >>> mind == blown True

mailslot 9y ago
Thanks! I didn't know I had literal string interpolation available until today!
dozzie 9y ago
Ah yes, the thing we had in shell, Perl, and Ruby since forever, and that was never a very good idea.
- odonnellryan 9y ago
  Why wasn't it a good idea in these languages?
  - dozzie 9y ago
    Because it's often hard to edit (which includes quoting or decoding where computation or variable starts) and because it mixes formatting and presenting data with computation.
tedmiston 9y ago
You can do cool nested calls with them too. >>> class A: ... def __init__(self): ... self.foo = 5 ... def bar(self): ... return 'cake' ... >>> a = A() >>> f'{a.foo}' '5' >>> f'{a.bar()}' 'cake' >>> x = {'b': 1, 'c': 2} >>> f"{x['b']}" '1'
- tudelo 9y ago
  Interesting. Thanks for the post. I always just concatenated them out of laziness, and this looks even lazier.
  - odonnellryan 9y ago
    It's super nice when you're working on reporting software: software that needs to quickly shoot out a string like this from time-to-time! It's much nicer to write this: f"{account_name} {pretty_date(start_date)} - {pretty_date(end_date)} account attribution" and MUCH easier to maintain than the alternative...!
- pyedpiper 9y ago
  saw this after posting, so epicly useful. Alreadying thinking of some nice concise, explanatory custom Exception descriptions..
in9 9y ago
it is very very true. F-strings are awesome. But there is one use case that I prefer .format(), and is when formatting a string using a dictionary. Being able to is awesome: some_long_string_template.format(**some_dictionary_with_many_keys) For me that is such a nice and practical use case. But yes for not many local variables, f-string is the way to go.
- EnderMB 9y ago
  I've only recently started learning Python, and the f-strings remind me a bit of the syntactic sugar provided by C# for string.Format() (var str = $"Hello, my name is {name}."; // for those who care) I get the same feeling as well, and it's something I noticed a lot when it was a new feature to C#. Suddenly, everyone abandoned string.Format() in favour of $"", even when the code would lose a lot of readability. Syntactic sugar is good and all, but I find it better to be more verbose for the sake of clarity.
kristoff_it 9y ago
Templated strings are great for when, as the name suggests, you want to create a string with some placeholders to be expanded at a later time. When you just want to interpolate a string on the fly, Fstrings are absolutely the right thing to do most of the time.
- pyedpiper 9y ago
  true but it seems that the performance gap is pretty huge and the new f-strings actually come in on top for string substitution: https://cito.github.io/blog/f-strings/ https://cito.github.io/blog/f-strings/
jxub 9y ago
You could also do: "text {}".format(foo) Works in Python 3.5 and earlier ones too.

15 points by pyedpiper 9y ago

mailslot 9y ago

Thanks! I didn't know I had literal string interpolation available until today!

dozzie 9y ago

Ah yes, the thing we had in shell, Perl, and Ruby since forever, and that was never a very good idea.

odonnellryan 9y ago
Why wasn't it a good idea in these languages?
- dozzie 9y ago
  Because it's often hard to edit (which includes quoting or decoding where computation or variable starts) and because it mixes formatting and presenting data with computation.

tedmiston 9y ago

You can do cool nested calls with them too. >>> class A: ... def __init__(self): ... self.foo = 5 ... def bar(self): ... return 'cake' ... >>> a = A() >>> f'{a.foo}' '5' >>> f'{a.bar()}' 'cake' >>> x = {'b': 1, 'c': 2} >>> f"{x['b']}" '1'

tudelo 9y ago
Interesting. Thanks for the post. I always just concatenated them out of laziness, and this looks even lazier.
- odonnellryan 9y ago
  It's super nice when you're working on reporting software: software that needs to quickly shoot out a string like this from time-to-time! It's much nicer to write this: f"{account_name} {pretty_date(start_date)} - {pretty_date(end_date)} account attribution" and MUCH easier to maintain than the alternative...!
pyedpiper 9y ago
saw this after posting, so epicly useful. Alreadying thinking of some nice concise, explanatory custom Exception descriptions..

in9 9y ago

it is very very true. F-strings are awesome. But there is one use case that I prefer .format(), and is when formatting a string using a dictionary. Being able to is awesome: some_long_string_template.format(**some_dictionary_with_many_keys) For me that is such a nice and practical use case. But yes for not many local variables, f-string is the way to go.

EnderMB 9y ago
I've only recently started learning Python, and the f-strings remind me a bit of the syntactic sugar provided by C# for string.Format() (var str = $"Hello, my name is {name}."; // for those who care) I get the same feeling as well, and it's something I noticed a lot when it was a new feature to C#. Suddenly, everyone abandoned string.Format() in favour of $"", even when the code would lose a lot of readability. Syntactic sugar is good and all, but I find it better to be more verbose for the sake of clarity.

kristoff_it 9y ago

Templated strings are great for when, as the name suggests, you want to create a string with some placeholders to be expanded at a later time. When you just want to interpolate a string on the fly, Fstrings are absolutely the right thing to do most of the time.

pyedpiper 9y ago
true but it seems that the performance gap is pretty huge and the new f-strings actually come in on top for string substitution: https://cito.github.io/blog/f-strings/ https://cito.github.io/blog/f-strings/

jxub 9y ago

You could also do: "text {}".format(foo) Works in Python 3.5 and earlier ones too.