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Python Python Basics Types and Branching Comparisons

Luke Maschoff
Luke Maschoff
820 Points

In Python, what is the purpose of .format()?

Confused on what .format() does in Python.

2 Answers

Steven Parker
Steven Parker
210,425 Points

The "format" method looks through the string it is applied to for placeholder tokens (usually "{}"), and replaces each of them with one of the arguments passed to it. It's a good way to add data from variables into messages.

For more details, see the Custom String Formatting section of the Python reference manual.

Øyvind Andreassen
Øyvind Andreassen
16,839 Points

To elaborate on Steven's answer.

If you want to have a string formatted a certain way each time you could do something like this:

def favorite_food(name, food):
    return "Hi, I'm {name} and I love to eat {food}!".format(name=name, food=food)

So each time you call favorite_food you can pass in a name and a food and get the string you expect.

Steven Parker
Steven Parker
210,425 Points

If I understand what I just read in the manual link given above, keyword argments are now deprecated for "format". So refactoring that example for the current version might look like this:

def favorite_food(name, food):
    return "Hi, I'm {} and I love to eat {}!".format(name, food)
Øyvind Andreassen
Øyvind Andreassen
16,839 Points

Both solution will work, I haven't heard that keyword arguments are deprecated as they give very clear instructions on what should go where. Tested in Python 3.7.0.

With the f-strings in Python you can also do:

def favorite_food(name, food):
    return f"Hi, I'm {name} and I love to eat {food}!"

This article goes through pros and cons with all approaches.

Steven Parker
Steven Parker
210,425 Points

Take a look at the manual page I linked in the answer. It contains this:

Changed in version 3.7: A format string argument is now positional-only.

Am I misunderstanding that?

Mark Nembhard
Mark Nembhard
1,387 Points

Hi . the chat about the deprecated format is interesting. If you have quite a few place holders then having the names of the string variables that you want to place in them makes sense and less error prone. So instead of the .format(x,y,z) variables that have to go in sequential order you can just list the variable names and they will jump into the place-holders where they are mentioned. Please correct me if i am wrong as i am new to this

Steven Parker
Steven Parker
210,425 Points

The keyword arguments can be handy, and they do still work for now, but the manual says they are no longer "official". As to why they are moving away from them, I have no idea!