Thread by @mathsppblog

I have been tweeting about Python 🐍 string formatting.

I have been preaching 🙏 that f-strings are the best string formatting alternative.

Then comes the string method `.format`.

And only then, %-formatting.

Here is a thread 🧵 comparing the 3 👇

In its most basic form,

👉 %-formatting uses % and a letter inside the string
👉 `.format` replaces sequences of {} with the data
👉 f-strings use {} to insert the data _inside_ the string

Here is how it looks like 👇

An undervalued feature of string formatting is that you can easily determine whether your data should be formatted with its string (str) or with its representation (repr).

For debugging, `repr` is usually more useful.

Here is how this looks like 👇

Aligning the data inside a field is also much easier with `.format` and f-strings.

For one, %-formatting can't handle centre alignment.

Secondly, with `.format` and f-strings you just use <^>, which points to where the alignment should be!

Easy to remember 🤔💭✅

Now, to be fair, there are some situations when I think `.format` is better than f-strings.

Such an example is when we have the formatting data inside a dictionary, with string keys.

In that case, `.format` is great!

There is another situation in which `.format` and f-strings completely blow %-formatting out of the water.

With `.format` and f-strings, we can implement custom formatting specifiers for our own objects.

All we need is `__format__`!

Here is a (silly) demo 👇

These were just some comparison points between the three main ways of doing string formatting in Python.

I took these examples from a Pydon'ts article of mine, that you can read here 👇

mathspp.com/blog/pydonts/s…

I'm currently working on a string formatting case study.

What I mean is, I will take an old Python project that is used in real life...

But that uses only %-formatting.

And I will review the whole thing, upgrading the string formatting as I go.

Then, I will write a full article explaining

👉 what I did
👉 where I decided to use f-strings and where I decided to use `.format`
👉 why I made those decisions

Sounds interesting?

Then subscribe to my newsletter to stay in the loop 😉

mathspp.com/subscribe

TL;DR:

👉 f-strings are generally better than `.format`:
shorter & more expressive

👉 %-formatting should be avoided:
old & less features

👉 do modern alignment with <^>

👉 .format is nicer than f-strings when data is in a dictionary with string keys

See you around 👋