Photo by Nate Grant on Unsplash
The ability to format a string is a pretty basic requirement for anyone that can code, but, there’ve been more than a few ways in the past that you’ve been able to do this in Python. There’s the original % method, there’s the .format method and more recently, there’s the f-String method. So which do you choose?
I’m pretty lazy so once I got the hang of .format methods, I kind of stuck to them, but there are drawbacks that I’ll cover which signify the problem with them.
But first, let’s do a quick overview:
This is the classic method, where those who were coding in the early Python2 days will remember clearly. Essentially you add in a % score with an ‘s’ (to reflect you want to chuck in a string) and add the % sign after the string as follows.
>>> name = "John"
>>> "Hello, %s" % name
'Hello, John'
I mean the first problem is that it just seems a bit uncontrolled, and it’s also a bit annoying you have to specify what type.
To add more than one thing it becomes a bit annoying too as you introduce a tuple as follows:
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>>> "Hello, %s my age is %s." % (name, age)
which is fine, but once the strings get quite long, it can be difficult to keep track. Imagine a pre-calculated customer reply (something simple, but just a bit long), as follows:
>>> "Hey %s! Thanks for ordering with us today. We saw that your payment for order number %s didn't go through to the address %s. Can you verify that your mobile number: %s is correct?" % (name, order_number, address, mobile_number)
And it can only get worse from there.
>>> "Hello, {}. I am {}.".format(name, age)
'Hello, John. I am 44.'
and a bit more control as you can reference the variable you want by referencing their index:
And you can also do something a bit fancier:
>>> details = {'name': 'John', 'age': 44}
>>> "Hello, {name}. I am {age}.".format(name=details['name'], age=person['age'])
'Hello, John. You are 44.'
Imagine the case with 10 variables and a super long string, the result would still be no different to the % method.
f-Strings (or formatted string literals) are the latest way to manipulate strings in Python. Essentially you can actually place the variable into the string, if you follow a set of rules.
So for example, the above basic example now changes to:
>>> f"Hello, {name}. I am {age}."
'Hello, John. I am 44.'
Isn’t that much nicer?
Moreover, we can expand this functionality to put python expressions into f-strings:
>>> f"{3 * 3}"
'9'
or even:
>>> patient = 'David'
>>> f"Can the patient: {to_lowercase(name)} please come to the desk."
'Can the patient: David please come to the desk.'
So that’s cool! You can now incorporate expressions without too much difficulty, and this is just the beginning.
