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Joe Neville
Joe Neville

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Use Python f-strings and never look back!

โ“Are you using f-strings to format your strings in Python? Yes? Great.
๐Ÿš€ If not, consider dropping your tired old format approach and get with the new(ish) stuff: f-strings.
๐Ÿ“š There's plenty of blogs out there that tell you all about f-strings. They tell you at length about the old approaches, % formatting and .format(), so I'm not going to go over all that, I'm just here to encourage you to take a look at f-strings.
๐Ÿค” Why? I'm using f-strings all the time now, and .format() seems clunky and overly verbose in comparison.

Here's the basics:

  • f-strings is the name given to 'formatted string literals'
  • Python 3.6+
  • Similar in approach to .format() but less verbose, which helps keep your line length down and improve code readability.

A few examples

Here's a simple combination of string variable declaration and print using .format():

>>> device = "clocks"
>>> time = "thirteen"
>>> sentence = "The {} were striking {}".format(device, time)
>>> print(sentence)
The clocks were striking thirteen
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Now, the same code, but using f-string:

>>> device = "clocks"
>>> time = "thirteen"
>>> sentence = f"The {device} were striking {time}"
>>> print(sentence)
The clocks were striking thirteen
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Looking at the two approaches it doesn't seem like much of a difference. But I think the improvement are enough to make me switch to f-strings and never look back.

  • F-strings save you eight characters by using a single 'f' to declare that the code uses f-strings, rather than the '.format()'.
  • Writing code is more intuitive, I feel, adding the string variables within the string itself, rather than saving this for the end of the line.
  • Reading code is easier because the declarations are right there in the string, again, rather than at the end of the line.
  • N.B. .format does allow variables in the braces, but that has the additional requirement of having to declare those in the final brackets, like so:
sentence = "The {device} were striking {time}".format(
device=device, time=time
)
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As you can see, this approach is even more verbose.

In isolation, all this points may seem minor, but as string formatting is such a necessary part of so much Python code, these small improvements can make a big difference to the overall experience of reading and writing Python.

Some extra details

Quotation marks can be used within an f-string, as long as different types are used

>>> f'{"quoted string"}'
'quoted string'
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Methods can be called directly

>>> sentence = f"The {device.upper()} were striking {time}"
>>> print(sentence)
The CLOCKS were striking thirteen
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For more details, check out PEP 498, the proposal that was developed into f-strings here.

Give f-strings a go, I hope you find them as useful as I have.

Thanks for reading.

๐Ÿฆ @joeneville_

Top comments (7)

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evanroggenkamp profile image
Evan Roggenkamp

F strings are fantastic but format absolutely still has its uses. Named format placeholders allow dictionary expansion to dynamic arguments, for one, not to mention string formatting, alignment, etc. I agree for short concise strings, theyโ€™re excellent!

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joeneville_ profile image
Joe Neville Author

Good points, I didn't think about the alignment aspect as I was writing this. Thanks for the reminder.

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owluitar profile image
Matthew S. Emerson

I personally enjoy f-strings when using them to write formatted input files for different scientific analysis software.

Some softwares require input files with a specified column format, and others do not.
Having the ability to take an example input file, changing each parameter to an f-string that calls a variable stored in a dictionary in another file is very useful (especially for reproducibility in my case).

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chrisgreening profile image
Chris Greening

f-strings are one of my absolute favorite things in Python lol, gotta love expressive and concise code

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devzlx profile image
Zlx

true lol

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devzlx profile image
Zlx

To be honest, I like f strings because:

  1. They are compact
  2. Easier to remember
  3. Easier to understand

But I guess that if you want more uses then you can use formats

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joeneville_ profile image
Joe Neville Author

Good summary. I'm thinking along the same lines.

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