How can I use f-string with a variable, not with a string literal?

I want to use f-string with my string variable, not with string defined with a string literal, "...".

Here is my code:

name=["deep","mahesh","nirbhay"]
user_input = r"certi_{element}" # this string I ask from user  

for element in name:
    print(f"{user_input}")

This code gives output:

certi_{element}
certi_{element}
certi_{element}

But I want:

certi_{deep}
certi_{mahesh}
certi_{nirbhay}

How can I do this?

---

_{See also: How to postpone/defer the evaluation of f-strings?}

If you define:

def fstr(template):
    return eval(f"f'{template}'")

Then you can do:

name=["deep","mahesh","nirbhay"]
user_input = r"certi_{element}" # this string i ask from user  

for element in name:
    print(fstr(user_input))

Which gives as output:

certi_deep
certi_mahesh
certi_nirbhay

But be aware that users can use expressions in the template, like e.g.:

import os  # assume you have used os somewhere
user_input = r"certi_{os.environ}"

for element in name:
    print(fstr(user_input))

You definitely don't want this!

Therefore, a much safer option is to define:

def fstr(template, **kwargs):
    return eval(f"f'{template}'", kwargs)

Arbitrary code is no longer possible, but users can still use string expressions like:

user_input = r"certi_{element.upper()*2}"

for element in name:
    print(fstr(user_input, element=element))

Gives as output:

certi_DEEPDEEP
certi_MAHESHMAHESH
certi_NIRBHAYNIRBHAY

Which may be desired in some cases.