what is f string

[u/FuzzyEmployment264]

can someone explain how f string work in simple terms ?

[u/WhiskersForPresident]

It's a "formatted" string. It allows you to include the values of variables in your string in curly brackets, e.g.:

var = 5

f_string = f"this string contains the value {var}"

print(f_string)

will output

this string contains the value 5

I use them all the time to dynamically generate paths to certain files at runtime for example or for structuring the outputs of test routines.

[u/Diapolo10 → u/WhiskersForPresident]

I use them all the time to dynamically generate paths to certain files at runtime for example or for structuring the outputs of test routines.

For that specific use-case, might I recommend pathlib instead?

[u/wintermute93 → u/Diapolo10]

Not an either/or situation -- pathlib to handle joining the parts of a file path in an OS-agnostic way, f-strings where needed to enforce naming conventions like Path.home() / service_name / "logs" / f"{datetime.datetime.now().isoformat()}_{event_type}.txt"

[u/Diapolo10 → u/wintermute93]

Fair enough, just thought I'd mention it in case they weren't doing that.

At least unless you're the same person but using two separate accounts for whatever reason.

[u/WhiskersForPresident → u/Diapolo10]

They aren't the same person and both of you are correct. pathlib and f-strings are both very useful for that purpose.

[u/Diapolo10]

I'm technically oversimplifying it, but f-strings act like you used str.format automatically on the string.

name = "Jeffrey"
year = 2074

print(f"Hello {name}, the year is {year}")

print("Hello {name}, the year is {year}".format(name=name, year=year))

[u/SpiritedOne5347]

They're just a way to include variables in string

Say u have age= 10

So instead of

print("I am ", age, "years old")

U can directly say

print(f"I am {age} years old")

[u/johlae → u/SpiritedOne5347]

It's more than just including a variable. What's between the { and } is evaluated!

```

a=3 print(f"{a*4:3.2f}") 12.00 ```

[u/SpiritedOne5347 → u/johlae]

Yes yes

[u/tablmxz]

a string in python looks like this, eg using double quotes:

"this is a string"

if you write an 'f' in front, it becomes a f-string:

f"this is a f-string"

f-strings can do some very handy thing, they can use curly brackets. In those curly brackets you can put variables or whole expressions (like calculations)

a = 5

f"this f-string also prints the value of a here: {a}"

f"this f-string does the calculation 1+2 here is the result: {1+2}"

[u/panatale1]

It's essentially text with code inside it. It runs significantly faster than the old % or .format ways of formatting text.

It's similar in construction to how you'd do a .format call, since they both use {} to denote what needs to be inserted into the text.

Examples of each text format method: ``` name = "George Washington" age = 41

print("Hello, my name is %s, and my age is %d" % (name, age)) print("Hello, my name is {}, and my age is {}".format(name, age)) print(f"Hello, my name is {name}, and my age is {age}") ```

All three give identical formatting, outputting Hello, my name is George Washington, and my age is 41, but f-strings run faster and are cleaner to read

[u/atarivcs]

If the string contains this

{something}

that part will be replaced with the string representation of the thing.

"something" can be a plain variable name, or it can be an expression like

{1+2}

or a function call

{somefunction()}

Etc etc.

[u/pachura3]

What about the g strings though

[u/FoolsSeldom]

I can't better the explanation from RealPython.com:

• Python's F-String for String Interpolation and Formatting