Python F-string Formatting

Before Python 3.6, you had two options to format your strings:

• % formatting.
• str.format().

The F-string formatting option has been available since Python 3.6.

In this lesson, I’ll show you why the older % formatting and str.format() options to format your strings are obsolete nowadays and how the F-string formatting option makes your life much easier.

% Formatting

The %-formatting option has been available since the beginning of Python. The % operator is built into string objects. You can use this to format strings. For example:

You can use the % operator multiple times, but you’ll need to use a tuple () to supply the values you want to use to format your string:

If you only want to format your strings with one or two values, the % operator works fine. However, with many values to replace, your code becomes difficult to read:

In the code above, you can see the problem with the % operator. Your code becomes difficult to read because you can’t really tell which value replaces what % symbol.

str.format()

Python 3 has a newer way to format strings by using .format() on a string object. Here is a quick example that looks similar to the old %-formatting method.

It is possible to specify the values you want to use to format your strings within the strings:

This makes your code easier to read than the % formatting method. However, if you have many things in your string that you want to format, your code becomes messy:

F-Strings

F-strings are easy to work with and keep your code readable. Here is a quick example:

Before the string, you add an “f”. This can be a small or capital letter. You can then add whatever you want to format in between {}. A huge advantage of this way of formatting is that your code remains easy to read, even when you want to format many things in your string. For example:

Python Expressions

I used variables like “vendor” or “platform” with assigned strings in the examples above. Python evaluates f-strings at runtime, allowing you to run any valid Python expressions in a string. Here is an example:

In the example above, I use an arithmetic operator (division) in the f-string.

Here is one more example where I use the title() method:

Being able to use expressions in your code can help to keep your code nice and clean.

Conclusion

In this lesson, you have learned how f-strings work and why this is a better option than the %-operator or str.format() method. There is more that you can do with f-strings, but this should be enough to get you started. You can read more about it in PEP 498.

I hope you enjoyed this lesson. If you have any questions feel free to leave a comment!