Is there a way to unpack a dictionary into an f-string template?

Question

With .format we can unpack a dictionary into a string template. That’s the only thing I haven’t found how to do with f-strings.
Is there a way to do it?

E.g. how to do this with f-strings?

template = "my values: {number} {item}"
values = dict(number=1, item='box')

print(template.format(**values))

Edit:

I thought you can have f-string templates for undefined values with something like this, but it doesn’t work either:

template2 = "my values: {(number := None)} {(item := None)}" # values are immutable after defining
values = dict(number=1, item='box')

# how to unpack `values` into `template2`, is it possible?

I’m aware of the longer ways to do it, what I’m looking for is only whether it’s possible to use unpacking. Cheers!!

Asked By: Raider of the lost BBS

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Source

Answer 1

Not that I am aware of with f-strings, but there are string templates:

from string import Template

template = Template("my values: $number $item")
values = dict(number=1, item='box')

print(template.substitute(**values)) # my values: 1 box

Answered By: Mack Raymond

Answer 2

What’s wrong with these:

values = dict(number=1, item='box')
print(f"{values=}")
print(f"values= {values['number']} {values['item']}{values.get('missing')}")

which gets you:

values={'number': 1, 'item': 'box'}
values= 1 box None

Or do you want to declare your f-string before you’ve set up the dict and then plug in the dict? Sorry, no can do, f-strings get evaluated right away, they are not really pre-defined templates.

Pre-defined templates hack

I’ve worked a lot with templates, usually the %(foo)s kind or else Jinja2 templates and have missed the capability to pass templates around, when using f-strings.

This below is a hack, but it does allow doing that, after a fashion. Thought of doing that a while back, never tried it though.

def template_1(**values):
    number = values["number"]
    item = values["item"]
    missing = values.get("missing")    
    return f"values1= {number} {item} {missing}"

def template_2(**values):
    return f"values2= {values['number']} {values['item']} {values.get('missing')}"    

print(template_1(**values))

def do_it(t, **kwargs):
    return t(**kwargs)

print(do_it(template_2,missing=3, **values))

Output

values1= 1 box None
values2= 1 box 3

Answered By: JL Peyret

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