F-Strings Conclusion—Go Forth and Format!

Thanks for this. I will be using f-strings from here on.

Feel free to laugh, my way of doing things before was to do like this:

print(‘This is the start ‘+str(variable_name)+’ and this is the end.’)

If you ask me, this is more like f-strings in terms of how it reads than either %-formatting or the .format method. Maybe that is why I was intuitively drawn to it!

Thank You!

Thanks for this tutorial.

I would like to display a float number with a number of decimals specified as a function argument.

”% style” works:

def format(float_number, decimal_places):
    return '%.*f' % (decimal_places, float_number) 
    # format(pi, 2) returns 3.14; format(pi, 3) returns 3.142 etc.

But all attempts to accomplish this with f-strings have so far failed. For example, I tried this:

def format(float_number, decimal_places):
    specifier = f':.{decimal_places}f'
    return f'{float_number}{specifier}'
    # format(pi,2) returns 3.141592653589793:.2f

Everything else I’ve tried either just returns the number with format specifier appended, as above, or results in “ValueError: Invalid format specifier”.

Is it possible to replicate this functionality using an f-string?

Hi @amack604, yes you can do this with an f-string:

from math import pi

def format(float_number, decimal_places):
    return f'{float_number:.{decimal_places + 1}}'

format(pi, 2)  # 3.14
format(pi, 3)  # 3.142

There’s a LOT you can do with that string formatting mini-language, which I think you already know about. :)

For applying some of the specifiers in f-strings as variables, seems like you need to use another set of squiggly braces in order to input the value.

Thanks very much, Martin. Thought I’d tried the same nesting you used, but obviously not! :)

Interestingly, this code yields the same result as yours:

def format(float_number, decimal_places):
    return f'{float_number:.{decimal_places}f}'

Oh! Well that’s 100 times more beautiful than mine @amack604 😃

I did wonder about why I’d have to add 1 but was too lazy to play around with it more 😂…

Nice work! 🙌

Liked it! Gives tips and study guidance for those starting out. we learned the evolution of f’ in python writing, and how to make it as pythonic as possible and current.

If you would like to add a small disadvantage of f-strings, it is that they are immediate. If you wanted to send, say a string template and a dictionary into a function that would “apply” the f-string to the dictionary, it wont work. E.g. using f-strings for different ways of formatting a Date. There a .format would probably work better.

@Erik Dyrelius yes that’s a good point! They’re not helpful for templating. We’re currently updating the tutorial that this course is based and are also including that aspect. :)

A good intro to f-string. I’ll be using them from now on. I previously looked at the f-string dubiously and thought what they were. Now I know! Yayy!