Ffile: f-strings in a file

The thing you never asked for, but that you got anyway

What are f-strings?

Not sure how you got here without knowing that, but in short, its the new way to format strings in python as of 3.6! Which isn't that new. Its been out a while. Like google it, there are tons of resources on why f-strings are cool.

I know f-strings are cool, so whats this then?

You can do a single line f-strings like this:

name = 'Matt'
print(f"{name} is not the name of a good developer")

sublime

but multi-line f-strings are ugly:

name = "Matt"
adjective = "mediocre"
lines = [
    f"{name} is the name of some Browns fan. And they are a {adjective} football team.",
    "LAME!",
    "Not only that,"
    f"This dude {name.upper()} sounds like a {adjective.upper()} father!",
]
print("\n".join(lines))

Yikes! Harsh f-string! And that needed a real weird thing with new-lines.

Also, what if you want to parameterize a long file? Several hundred or thousand lines? No thanks.

F-strings on a file would be cool

Lets throw that text into a file, lets call it "template.txt" which coincidentally exists in this very repository:

{name} is a good developer!
His kids love him deeply because he is a {adjective} father!

They definitely do NOT say:

"Hey {name.upper()}! you are {adjective.split(' ')[-1]} at parenting!"
  - {name.lower()}'s kids, probably

Boy it would be cool to take a big complex document, parametrize it like an f-string, and even run some simple python in it!

template = Ffile("template.txt")
template.print(name="Matt", adjective="not bad")

sublime

Also, maybe just you don't want to print but instead you want that formatted string

formatted = template.f(name="Matt", adjective="not bad")

don't believe me? Well pip install this package:

pip install ffile

or from this repo:

pip install .

and then run:

python example.py

Don't leave yet! There is a CLI too!

You can also call ffile from the command line!

ffile template.txt --vars name=Matt adjective='not bad'

or you can put those variables in a json file:

ffile template.txt --json params.json

or what about yaml:

ffile template.txt --yaml params.yaml

Anything else?

There are a couple of clever ways of calling this. I think I found most of them, check out the tests!

Any concerns?

I know what you are thinking:

"Something... something... arbitrary code execution..."

• you, maybe

Probably. Don't use this where you let just anyone write the template file. Like, don't put this in front of a web form and let the internet run scripts. Or other things I haven't thought of. Don't do dumb things and it'll probably be fine.